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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 10-K

Commission file number: 001-16503

WILLIS GROUP HOLDINGS LIMITED
(Exact name of Registrant as specified in its charter)

        Indicate by check mark whether the Registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ý    No o

        Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the Registrant's knowledge, in definite proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. o

        Indicate by check mark whether Registrant is an accelerated filer (as defined in Rule 12b-2 of the Act). Yes ý    No o

        As of June 30, 2003, the aggregate market value of the voting stock held by non-affiliates of the Registrant was approximately $3,519,659,760.

        As of February 27, 2004, there were outstanding 156,275,020 shares of common stock, par value $0.000115 per share of the Registrant.

DOCUMENTS INCORPORATED BY REFERENCE

        Portions of Willis Group Holding Limited's 2004 Notice of Annual Meeting of Stockholders and Proxy Statement are incorporated by reference in the Form 10-K in response to Items in Part II and Part III.

WILLIS GROUP HOLDINGS LIMITED
ANNUAL REPORT ON FORM 10-K
FOR THE YEAR ENDED DECEMBER 31, 2003

Certain Definitions

        The following definitions apply throughout this annual report unless the context requires otherwise:

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Table Of Contents

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INFORMATION CONCERNING FORWARD-LOOKING STATEMENTS

        We have included in this document forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, that state our intentions, beliefs, expectations or predictions for the future. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from historical results or those anticipated, depending on a variety of factors such as changes in premium rates, the competitive environment, the actual cost of resolution of contingent liabilities, general economic conditions in different countries around the world, fluctuations in currency exchange rates and global equity and fixed income markets and other factors disclosed under "Risk Factors" and elsewhere in this document. Although we believe that the expectations reflected in forward-looking statements are reasonable we can give no assurance that those expectations will prove to have been correct. We assume no obligation to update our forward-looking statements or to advise of changes in the assumptions and factors on which they are based. All forward-looking statements contained or incorporated by reference in this document are qualified by reference to this cautionary statement.

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PART I

Item 1—Business

History and Development of the Company

        Willis Group Holdings is the ultimate holding company for the Group. We trace our history to 1828 and are one of the largest insurance brokers in the world.

        Willis Group Holdings was incorporated in Bermuda on February 8, 2001 as an exempted company under the Companies Act, for the sole purpose of redomiciling the ultimate parent company of the Willis Group (comprised of TA I Limited and subsidiaries) from the United Kingdom to Bermuda. On incorporation Willis Group Holdings was wholly-owned by Profit Sharing (Overseas), Limited Partnership, an affiliate of KKR and one of the existing shareholders of TA I Limited ("TA I").

        Willis Group Holdings, effective from May 8, 2001, exchanged its Shares for all the issued and outstanding ordinary shares of TA I. On April 10, 2001, Willis Group Holdings made an offer to exchange one of its non-voting management common shares for each outstanding non-voting management ordinary share of TA I. The non-voting management shares issued by Willis Group Holdings automatically converted into voting shares on consummation of the Willis Group Holdings' initial public offering. In addition, all management ordinary stock options of TA I were rolled over into identical stock options of Willis Group Holdings. As a consequence of these transactions, Willis Group Holdings is the beneficial owner of 100% of TA I's issued and outstanding share capital.

        Willis Group Holdings completed an initial public offering of approximately 16% of its Shares in June 2001. In November 2001, May 2002, April 2003 and February 2004 approximately 12%, 15%, 16% and 15% respectively, of the Shares were publicly sold through secondary public offerings.

        For administrative convenience, we utilize the offices of a subsidiary company as our principal executive offices. The address is:

Willis Group Holdings Limited
c/o Willis Group Limited
Ten Trinity Square
London EC3P 3AX
England
Tel: +44-20-7488-8111

        In recent years, we have completed a number of acquisitions and dispositions as part of our efforts to focus our operations out of non-core or non-profitable businesses and to expand our global capabilities. During 2003, we increased our ownership of Willis Iberia Correduria de Seguros y Reaseguros S.A. ("Willis Iberia") to 77%, with our French associate, Gras Savoye & Company ("Gras Savoye"), owning the remaining 23%; acquired the remaining 22% interest in Willis GmbH & Co., K.G., Germany's third largest insurance broker and increased our holding in Willis Italia Holdings S.r.l. to 100%. In 2003, we acquired two California brokers, Cogdill Bonding and Insurance Services, Inc. and T.C.T. Insurance Services, Inc. and the business of River City Agency, an insurance agency based in Minnesota. In the second quarter of 2003 we formed a joint venture in India, Willis BA India Private Limited, with Bhaichand Amoluk Consultancy Services Pvt. Ltd. to provide insurance broking and risk management services in India. Finally, in January 2004 we acquired Ital Re S.p.A., a major Italian reinsurance broker, the remaining 70% of our interest in Willis A/S, Denmark's largest insurance broker and Kirecon A/S, a leader in providing reinsurance broking services in Denmark as well as the business of Vision Insurance Group, a risk management and reinsurance brokerage firm based in Alabama.

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Available Information

        As of December 31, 2002 a majority of the Shares were for the first time held by US residents and the Company ceased to be a "foreign private issuer" for US reporting purposes. Accordingly, the Company ceased filing Form 20-F annual reports and Form 6-K quarterly reports and now files Form 10-K annual reports and Form 10-Q quarterly reports. Our wholly-owned subsidiary, Willis Group Limited, however, which had publicly registered debt securities outstanding, filed its annual reports on Form 20-F and its quarterly reports on Form 6-K.

        Willis Group Holdings files annual, quarterly and current reports, proxy statements and other information with the Securities and Exchange Commission (the "SEC"). You may read and copy any documents we file at the SEC's public reference room at 450 Fifth Street, NW, Washington D.C. 20549. Please call the SEC at 1-800-SEC-0330 for information on the public reference room. The SEC maintains a website that contains annual, quarterly and current reports, proxy statements and other information that issuers (including Willis Group Holdings) file electronically with the SEC. The SEC's website is www.sec.gov.

        The Company makes available, free of charge through our website at www.willis.com our annual report on Form 10-K, our quarterly reports on Form 10-Q, current reports on Form 8-K, and Forms 3, 4, and 5 filed on behalf of directors and executive officers, as well as any amendments to those reports filed or furnished pursuant to the Securities Exchange Act of 1934 (the "Exchange Act") as soon as reasonably practicable after such material is electronically filed with, or furnished to, the SEC.

        The Company's Corporate Governance Guidelines, Audit Committee Charter, Compensation Committee Charter and Corporate Governance and Nominating Committee Charter are also available on our website or upon written or verbal request. Requests for copies of these documents should be directed in writing to the Company Secretary, Willis Group Holdings Limited, c/o Willis Group Limited, Ten Trinity Square, London EC3P 3AX, England or by telephone to +44 20 7481 7004.

General

        The Company provides a broad range of value-added risk management consulting and insurance brokerage services to in excess of 50,000 clients worldwide. We have significant market positions in the United States, in the United Kingdom and, directly and through our associates, in many other countries. We are one of three recognized leaders in providing specialized risk management advisory and other services on a global basis to clients in various industries including the aerospace, marine, construction and energy industries. In our capacity as an advisor and insurance broker, we act as an intermediary between our clients and insurance carriers by advising our clients on their risk management requirements, helping clients determine the best means of managing risk, and negotiating and placing insurance risk with insurance carriers through our global distribution network.

        We assist clients in the assessment of their risks, advise on the best ways of transferring suitable risk to the global insurance and reinsurance markets and then execute the transactions at the most appropriate available price, terms and conditions for our clients. Our global distribution network enables us to place the risk in the most appropriate insurance or reinsurance market worldwide. We also offer clients a broad range of services to help them to identify and control their risks. These services range from strategic risk consulting (including providing actuarial analyses), to a variety of due diligence services to the provision of practical on-site risk control services (such as health and safety or property loss control consulting). We also assist clients in planning how to manage incidents or crises when they occur. These services include contingency planning, security audits and product tampering plans. We are not an insurance company and therefore we do not underwrite insurance risks for our own account.

        We and our associates serve a diverse base of clients located in approximately 180 countries. These clients include major multinational and middle-market companies in a variety of industries, as well as

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public institutions. Many of our client relationships span decades. With approximately 14,500 employees around the world and a network of about 300 offices in some 80 countries, in each case including our associates, we believe we are one of only three insurance brokers in the world possessing the global operating presence, broad product expertise and extensive distribution network necessary to meet effectively the global risk management needs of many of our clients.

Business Strategy

        Our strategic objectives are to continue to grow revenues, cash flow and earnings and to enhance our position as one of the largest global providers of risk management services. We will build on our areas of strength and eliminate areas in which we do not see the opportunities for strong profitable growth. The key elements of this strategy are to capitalize on a strong, global franchise, emphasize our value-added services, focus on cross-selling our services, increase operating efficiencies, implement global best practices and create a single company culture. We also pursue strategic acquisitions and investments to strengthen our global franchise.

Our Business

        Insurance is a global business, and its participants are affected by global trends in capacity and pricing. Accordingly, we operate as one global business which ensures all clients' interests are handled efficiently and comprehensively, whatever their initial point of contact. We organize our business into three main areas: Global, North America and International. For information regarding revenues by geographic locations, see footnote 16 to the Consolidated Financial Statements contained herein.

Global

        Our Global business provides specialist brokerage and consulting services to clients worldwide for the risks arising from specific industrial and commercial activities. In these operations, we have extensive specialized experience handling diverse lines of coverage, including complex insurance programs, and acting as an intermediary between retail brokers and insurers. We increasingly provide consulting services on risk management with the objective of assisting clients to reduce the overall cost of risk. Our Global business serves clients in around 180 countries, primarily from United Kingdom offices, although we also serve clients from offices in the United States, Continental Europe and Asia.

        The Global business is divided into Global Specialties, Global Markets, Willis Reinsurance and Willis UK.

        Global Specialties has strong global positions in aerospace, marine, construction and several niche businesses. In aerospace we are highly experienced in the provision of insurance and reinsurance brokerage and risk management services to aerospace clients, including aircraft manufacturers, air cargo handlers and shippers, airport managers and other general aviation companies. Advisory services provided by aerospace include claims recovery, contract and leasing risk management, safety services and markets information. Aerospace is also a leading reinsurance broker of aerospace risks. Aerospace's clients are spread throughout the world and include over 250 airlines and nearly 40% of the world's leading insured non-American airports by passenger movement. Aerospace is also prominent in supplying the space industry through providing insurance and risk management services to over 40 companies. Other clients include those introduced from other intermediaries as well as insurers seeking reinsurance.

        We provide marine insurance and reinsurance brokerage services, including hull, cargo and general marine liabilities. Marine's clients include direct buyers, other insurance intermediaries and insurance and reinsurance companies. Marine insurance brokerage is our oldest line of business dating back to our establishment in 1828. Other services of marine include claims collection and recoveries.

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        The construction practice provides risk management advice and places cover for a wide range of UK and international construction activities. These range from domestic home buildings to such major complex projects such as Hong Kong's Chek Lap Kok airport and the deactivation of the Chernobyl nuclear power plant.

        We have three niche business areas: Fine Art, Jewelry, and Specie; Special Contingency Risks and Hughes-Gibb.

        The Fine Art, Jewelry, and Specie unit provides specialist risk management and insurance services to fine art, diamond and jewelry businesses and operators of armored cars. Coverage is also obtained for vault and bullion risks. The Special Contingency Risks unit specializes in producing packages to protect corporations, groups and individuals against special contingencies such as kidnap and ransom, extortion, detention, political repatriation and product contamination. The Hughes-Gibb unit principally services the insurance needs of the horse racing and horse breeding industry and also arranges the reinsurance of horse racing and horse breeding-related business for insurers worldwide.

        Global Markets comprises Global Markets North America, Global Markets International, Global Markets Financial Solutions, Willis Energy, Willis Professional Risks and Carrier Relations. Global Markets North America develops global solutions and marketing capability for all our businesses based in North America and Bermuda. The core areas of focus are property, casualty and management liability risks. Global Markets International works closely with the Willis UK and International retail networks to further develop access to global markets, and provide structuring and placing skills in the relevant areas of property, casualty and management liability. Global Markets Financial Solutions specializes in strategic risk assessment, transactional risk transfer and alternative risk financing solutions. It incorporates our political risk unit, as well as structured finance and credit teams. Willis Energy provides insurance brokering services, including property damage, liability, control of well and pollution insurance, to the energy industry. Willis Professional Risks specializes in brokering directors' and officers' insurance as well as professional indemnity insurance for corporations and professional firms. It also brokers structured crime and specialist liability insurance for clients across the broad spectrum of financial solutions. Finally, Carrier Relations analyzes, oversees and coordinates our Group activities and relationships with underwriting markets globally.

        We are one of the world's largest intermediaries for reinsurance and have a significant market share in many of the major markets. We are the largest marine and aviation reinsurance broker servicing the Japanese insurance sector. In the reinsurance area, we provide clients, both insurance and reinsurance companies, with a complete range of transactional capabilities as well as analytical and advisory services such as hazard modeling, financial and balance sheet analysis and reinsurance optimization studies. We also have a consulting unit, which markets its capabilities in actuarial and hazard modeling, as well as knowledge of the financial implications of catastrophe losses.

        Willis UK offers risk management and brokering services to corporate clients and individuals through approximately 17 offices. Each office services its own clients accessing the Group's global resources as appropriate to suit the clients' requirements. This unit also includes Willis Risk Solutions, which arranges tailored solutions for major companies, including several constituents of the UK FTSE 250 and the Willis Commercial Network which comprises franchise partnerships with nearly 60 privately-owned local UK insurance brokers and is designed to enable these brokers to meet the insurance requirements of small companies and individuals.

North America

        Our North America business provides risk management, insurance brokerage and related services to a wide variety of clients in the United States and Canada. In addition, we supply specialist consulting and brokerage services, including construction; employee benefits; healthcare; and advanced risk management services. Our North America business operates through a network of more than 80 offices

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located in 35 states in the United States and six offices in Canada. Certain parts of our Global business also have operations in the United States.

        The North America business comprises both our large account and middle market units which were brought together in early 2003. This amalgamation enables us to service our clients and present ourselves to prospects in a consistent manner, without regard for the size, geography or industry of the audience.

        The construction division specializes in providing risk management, insurance and surety bonding services to the construction industry. This division provides services to around one-quarter of the Engineering New Record Top 400 contractors (a listing of the largest 400 North American contractors based on revenue). It also has many of the largest US homebuilders as clients. The employee benefits division helps clients with the design and implementation of benefits and compensation plans.

        Healthcare provides insurance and consulting services to local healthcare professionals in the United States. Our North America advanced risk management services division provides actuarial consulting, captive management services and a wide range of other risk consulting activities to large clients.

        In addition, we provide specialist expertise to clients and insurance underwriters through other practices operating through expert staff located throughout the North American network. These practices include environmental risk, financial and executive risk and marine risk. Customer support facilities, which we refer to as centers of excellence, provide fast, focused and tailored support services to clients from Nashville, Tennessee and Phoenix, Arizona.

        We also have a wholesale unit that provides specialist services to the US insurance industry. The major entity within the unit is Stewart Smith which assists brokers by offering advice and expertise in property, casualty, professional and excess and surplus lines insurance placements in a variety of industries, including manufacturing, hospitality, real estate/habitational, transportation, construction, technology, entertainment and social services.

International

        Our International unit consists of a network of subsidiaries and associates other than those in North America, the United Kingdom and Republic of Ireland. This operation is located in 70 countries worldwide, including 20 countries in Europe, 14 in the Asia/Pacific region and 36 elsewhere in the world. The services provided are focused according to the characteristics of each market and are not identical in every office, but generally include direct risk management and insurance brokerage, specialist and reinsurance brokerage and employee benefits consulting.

        We believe the combined total revenues of our International subsidiaries and associates provide an indication of the spread and capability of our International network. In 2003, combined total revenues of our International subsidiaries and our associates were $714 million compared to $540 million in 2002. Our consolidated total revenues for 2003 only include the revenues of our International subsidiaries of $332 million and do not include the revenues of our associates of $382 million.

        As part of our on-going strategy, we have significantly strengthened International's market share and operations through a number of acquisitions and strategic investments in recent years. The most significant of these is the 33% interest in Gras Savoye, France's leading insurance broker. In 2003, we increased our investment in Willis GmbH to 100% and increased the ownership in Willis Iberia to 77% with our French associate, Gras Savoye, owning the remaining 23%. In 2004, we acquired Ital Re S.p.A., a major Italian reinsurance broker, and Kirecon A/S, a leader in providing reinsurance brokerage services in Denmark as well as the remaining 70% interest in Willis A/S, Denmark's largest insurance broker.

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        The following is a list of the major International associate investments currently held by us and our interest as of December 31, 2003:

(1)

Increased to 100% in January 2004.

        In connection with many of our investments, we retain rights to increase our ownership percentage over time, typically to a majority or 100% ownership position. In addition, in certain instances our co-shareholders have a right, typically based on some price formula of revenues or earnings, to put some or all of their shares to us. See Item 7 "Management's Discussion and Analysis of Financial Condition and Results of Operations".

        In addition to our strategic investments in associates, we have acquired a controlling interest in a broad geographic spread of other brokers. The following is a list of the significant International subsidiaries in which we have a controlling interest and our interest as of December 31, 2003:

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(1)

We have a 50.1% interest in the company.

Customers

        Our customers operate on a global and local scale in a multitude of businesses and industries throughout the world and generally range in size from major multinational corporations to middle market companies. Further, many of our client relationships span decades, for instance our relationship with The Tokio Marine and Fire Insurance Company, Limited dates back over 100 years. No one client accounted for more than 10% of revenues for fiscal year 2003. Additionally, we place insurance with over 5,000 insurance carriers, none of which individually accounted for more than 9% of the total premiums we placed on behalf of our clients in 2003.

Competition

        We face competition in all fields in which we operate. According to the July 2003 edition of Business Insurance, the 175 largest commercial insurance brokers globally reported brokerage revenues totalling $26.7 billion in 2002. The insurance brokerage industry, having recently gone through a period of rapid consolidation, is led by three global participants: Marsh & McLennan Companies, Inc., with approximately 31% of the worldwide market in 2002 referred to above; Aon Corporation, with approximately 23% of the worldwide market in 2002; and us, with approximately 7% of the worldwide market in 2002. The industry is highly fragmented beyond these three brokers, with the next largest broker having approximately 4% of the worldwide market.

        Competition in the insurance brokerage and risk management businesses in general is based on global capability, product breadth, innovation, quality of service and price. Our global capability and product breadth is similar to those of the two other global brokers, and thus we compete with them primarily based on innovation, quality of service and price. In addition, we compete with numerous specialist, regional and local firms. Insurance companies also compete with our brokers by directly soliciting insureds without the assistance of an independent broker or agent. Competition for premiums is intense in all our business lines and in every insurance market. Competition on premium rates has also exacerbated the pressures caused by a continuing reduction in demand in some classes of business. For example, insurers are currently retaining a greater proportion of their risk portfolios than previously. Industrial and commercial companies are increasingly relying upon captive insurance companies, self-insurance pools, risk retention groups, mutual insurance companies and other mechanisms for funding their risks, rather than buying insurance. We and our competitors provide management and similar services for those alternative risk transfer programs. Additional competitive

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pressures arise from the entry of new market participants, such as banks, accounting firms and insurance carriers themselves, offering risk management or transfer services. Our market share has been stable in recent years. We believe that our strategies of building on our strong global franchise, expanding on our employee benefit capabilities, increasing our operating efficiencies and creating a single company culture will allow us to retain and gain clients in the competitive marketplace. We also believe that our market position will provide us with opportunities to acquire smaller companies with strong regional presence or specialized expertise.

Regulation

        The manner in which we conduct our business is subject to legal requirements and governmental and quasi-governmental regulatory supervision in the various countries in which we operate. These requirements are generally designed to protect our clients by establishing minimum standards of conduct and practice, particularly regarding the provision of advice and product information as well as financial criteria.

        In the United Kingdom, our business activities are regulated by the General Insurance Standards Council, as well as by the Financial Services Authority, which also conducts monitoring visits to assess our compliance with their requirements. Further, our clients have the right to file complaints with our regulators about our services, and the regulators may conduct an investigation or require us to conduct an investigation into these complaints. Our failure, or that of our employees, to satisfy the regulators that we are in compliance with their requirements or the legal requirements governing our activities, can result in disciplinary action, fines, reputational damage and financial harm. Lloyd's, whose regulatory responsibilities for our insurance broking activities in the United Kingdom were transferred to the General Insurance Standards Council on July 3, 2000, other than for complaints that arose prior to that date, has disciplined and fined a number of Lloyd's brokers and their employees for misconduct. This misconduct covered failures to maintain procedures and records and to act in the clients' best interests, particularly in the taking of commissions without appropriate disclosure.

        The European Union Insurance Mediation Directive was adopted on September 30, 2002 and all European Union member states will have to implement the Directive by January 2005. The Directive introduces rules to enable insurance and reinsurance intermediaries to operate and provide services within each member state of the EU on a basis consistent with the EU single market and customer protection aims. Each EU member state is required to ensure that the insurance and reinsurance intermediaries resident in their country are registered with a statutory body in that country and that each intermediary meets professional requirements in relation to their competence, good repute, professional indemnity cover and financial capacity. In the United Kingdom the statutory body will be the Financial Services Authority and as a consequence, after January 14, 2005, such body will replace the General Insurance Standards Council and will become the sole regulator over insurance and reinsurance intermediary activities in the United Kingdom.

        HM Treasury, whose regulatory functions have been delegated to the Financial Services Authority, will continue to regulate Sovereign Marine & General Insurance Company Limited (In Scheme of Arrangement) ("Sovereign") as an insurance company.

        Our activities in connection with insurance brokerage services within the United States are subject to regulation and supervision by state authorities. Although the scope of regulation and form of supervision may vary from jurisdiction to jurisdiction, insurance laws in the United States are often complex and generally grant broad discretion to supervisory authorities in adopting regulations and supervising regulated activities. That supervision generally includes the licensing of insurance brokers and agents and the regulation of the handling and investment of client funds held in a fiduciary capacity. Our continuing ability to provide insurance brokerage in the jurisdictions in which we

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currently operate is dependent upon our compliance with the rules and regulations promulgated from time to time by the regulatory authorities in each of these jurisdictions.

        All companies carrying on similar activities in a given jurisdiction are subject to that regulation, and we do not consider that these controls adversely affect our competitive position.

Employees

        As of December 31, 2003 we had approximately 11,000 employees worldwide of whom approximately 3,440 and 3,560 were employed in the United Kingdom and the United States, respectively, with the balance of approximately 4,000 being employed across the rest of the world.

Risks Relating to our Business

        This section describes the material risks affecting the Group's business. These risks could materially affect the Group's business, its revenues, operating income, net income, net assets and liquidity and capital resources and, accordingly should be read in conjunction with any forward-looking statements in this Annual Report on Form 10-K.

Premiums and Commissions—We do not control the premiums on which our commissions are based, and volatility or declines in premiums may seriously undermine our profitability.

        We derive most of our revenues from commissions and fees for brokering and consulting services. We do not determine insurance premiums on which commissions are generally based. Premiums are cyclical in nature and may vary widely based on market conditions. From the late 1980s through late 2000, insurance premium rates generally declined as a result of a number of factors, including the expanded underwriting capacity of insurance carriers; consolidation of both insurance intermediaries and insurance carriers; and increased competition among insurance carriers.

        In addition, as traditional risk-bearing insurance carriers continue to outsource the production of premium revenue to non-affiliated agents or brokers such as ourselves, those insurance carriers may seek to reduce further their expenses by reducing the commission rates payable to those insurance agents or brokers. The reduction of these commission rates, along with general volatility and/or declines in premiums, may significantly undermine our profitability.

Claims, Lawsuits and Proceedings—Our business, results of operations, financial condition or liquidity may be materially adversely affected by errors and omissions and the outcome of certain actual and potential claims, lawsuits and proceedings.

        We are subject to various actual and potential claims, lawsuits and proceedings relating principally to alleged errors and omissions in connection with the placement of insurance and reinsurance in the ordinary course of business. Because we often assist our clients with matters, including the placement of insurance coverage and the handling of related claims, involving substantial amounts of money, errors and omissions claims against us may arise which in turn allege our potential liability for all or part of the amounts in question. Claimants can seek large damage awards and these claims can involve potentially significant defense costs. Such claims, lawsuits and proceedings could, for example, include allegations of damages for our employees or sub-agents failing, whether negligently or intentionally, to place coverage or notify claims on behalf of clients, to provide insurance carriers with complete and accurate information relating to the risks being insured or to appropriately apply funds that we hold for our clients on a fiduciary basis. We have established provisions against these items which we believe to be adequate in the light of current information and legal advice, and we adjust such provisions from time to time according to developments.

        While most of the errors and omissions claims made against us have, subject to our self-insured deductibles, been covered by our professional indemnity insurance, our business, results of operations,

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financial condition and liquidity may be adversely affected if in the future our insurance coverage proves to be inadequate or unavailable or there is an increase in liabilities for which we self-insure. In addition, claims, lawsuits and proceedings may harm our reputation or divert management resources away from operating our business.

        The principal actual or potential claims, lawsuits and proceedings to which we are currently subject are (i) claims relating to services provided by one of our UK subsidiaries, Willis Faber (Underwriting Management) Limited, to another subsidiary, Sovereign, that was engaged in insurance underwriting prior to 1991 as well as certain third party insurance companies; (ii) potential claims which could be asserted with respect to our placement of property and casualty insurance for a number of entities which were directly impacted by the September 11, 2001 destruction of New York's World Trade Center complex; (iii) potential claims arising out of various legal proceedings between reinsurers, reinsureds and their reinsurance brokers relating to personal accident excess of loss reinsurance placements for the years 1993 to 1998; and (iv) claims relating to activities by a US subsidiary of ours, Baccala and Shoop Insurance Services, prior to 1984 for certain insurance issuing companies. See Item 3 "Legal Proceedings".

Regulation—We are subject to insurance industry regulation worldwide. If we fail to comply with regulatory requirements, we may not be able to conduct our business.

        Many of our activities are subject to regulatory supervision in the various countries and jurisdictions in which we are based or our activities are undertaken. We have in the past failed to comply with some of these regulations and future failures to comply by us or our employees may occur. While past failures have resulted in insignificant fines, any failures reported in the future could lead to disciplinary action, including requiring clients to be compensated for loss, the imposition of more substantial fines and the possible revocation of our authorization to operate as well as reputational damage. In addition, changes in legislation or regulations and actions by regulators, including changes in administration and enforcement policies, could from time to time require operational improvements or modifications at various locations which could result in higher costs or hinder our ability to operate our business. See Item 1 "Business—Regulation".

Put and Call Arrangements—We have entered into significant put and call arrangements which may require us to pay substantial amounts to purchase shares in one of our associates. Those payments would reduce our cash flow and the funds available to grow our business.

        In connection with many of our investments in our associates, we retain rights to increase our ownership percentages of these associates over time and, in some cases, the existing owners also have a right to put their shares to us. The put arrangement in place for shares of our associate, Gras Savoye, may require us to pay substantial amounts to purchase those shares, which may cause a significant decrease in our liquidity and the funds available to grow our business. See Item 7 "Management's Discussion and Analysis of Financial Condition and Results of Operations".

        The rights under the put arrangement may be exercised through 2011, and if fully exercised, we would be required to buy shares of Gras Savoye, other than those held by its management, possibly increasing our ownership interest by 57% from 33% to 90%. Management shareholders of Gras Savoye, representing approximately 10% of the outstanding shares, do not have general put rights before 2011, but have certain put rights on their death, disability or retirement. Payments in connection with management put rights would not have exceeded $56 million if those rights had been fully exercised at December 31, 2003.

        Until 2005, the incremental 57% of Gras Savoye may be put to us at a price equal to the greater of approximately 800 million French francs ($154 million at December 31, 2003 exchange rates) or a price determined by a contractual formula based on earnings and revenue, which at December 31, 2003 would have amounted to approximately $319 million. After 2005, the put price is determined solely by

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the formula. The shareholders may put their shares individually at any time during the put period. The amounts we may have to pay in connection with the put arrangements may significantly exceed these estimates.

Competition—Competition in our industry is intense, and if we are unable to compete effectively, we may lose market share and our business may be materially adversely affected.

        We face competition in all fields in which we operate, based on global capability, product breadth, innovation, quality of service and price. We compete with Marsh & McLennan and Aon, the two other providers of global risk management services, as well as with numerous specialist, regional and local firms. If we are unable to compete effectively against these competitors, we will suffer lower revenue, reduced operating margins and loss of market share.

        Competition for business is intense in all our business lines and in every insurance market, and the other two providers of global risk management services have substantially greater market share than we do. Competition on premium rates has also exacerbated the pressures caused by a continuing reduction in demand in some classes of business. For example, insureds have been retaining a greater proportion of their risk portfolios than previously. Industrial and commercial companies have been increasingly relying upon their own subsidiary insurance companies, known as captive insurance companies, self-insurance pools, risk retention groups, mutual insurance companies and other mechanisms for funding their risks, rather than buying insurance. Additional competitive pressures arise from the entry of new market participants, such as banks, accounting firms and insurance carriers themselves, offering risk management or transfer services. See Item 1 "Business—Competition".

Dependence on Key Personnel—The loss of any member of our senior management, particularly our Chairman and Chief Executive Officer, or a significant number of our brokers could negatively affect our financial plans, marketing and other objectives.

        The loss of or failure to attract key personnel could significantly impede our financial plans, growth, marketing and other objectives. Our success depends to a substantial extent not only on the ability and experience of our senior management, particularly our Chairman and Chief Executive Officer, Joseph J. Plumeri, but also on the individual brokers and teams that service our clients and maintain client relationships. The insurance brokerage industry has in the past experienced intense competition for the services of leading individual brokers and brokerage teams, and we have lost key individuals and teams to competitors in the past. We believe that our future success will depend in large part on our ability to attract and retain additional highly skilled and qualified personnel and to expand, train and manage our employee base. We may not be successful in doing so, because the competition for qualified personnel in our industry is intense.

International Operations—Our significant non-US operations, particularly those in the United Kingdom, expose us to exchange rate fluctuations and various risks that could impact our business.

        A significant portion of our operations is conducted outside the United States. Accordingly, we are subject to legal, economic and market risks associated with operating in foreign countries, including devaluations and fluctuations in currency exchange rates; imposition of limitations on conversion of foreign currencies into pounds sterling or dollars or remittance of dividends and other payments by foreign subsidiaries; hyperinflation in certain foreign countries; imposition or increase of investment and other restrictions by foreign governments; and the requirement of complying with a wide variety of foreign laws.

        We report our operating results and financial condition in US dollars. Our US operations earn revenue and incur expenses primarily in dollars. In the United Kingdom, however, we earn revenue in a number of different currencies, but expenses are almost entirely incurred in pounds sterling. Outside

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the United States and the United Kingdom, we predominantly generate revenue and expenses in the local currency. The table below details the breakdown of revenues and expenses by currency in 2003.

        Because of devaluations and fluctuations in currency exchange rates or the imposition of limitations on conversion of foreign currencies into dollars, we are subject to currency translation exposure on the profits of our operations, in addition to economic exposure. Furthermore, the mismatch between sterling revenues and expenses creates an exchange exposure. As the pound sterling strengthens, the dollars required to be translated into pounds sterling to cover the net sterling expenses increase, which then causes our results to be negatively impacted. Given these facts, the strength of the pound sterling relative to the US dollar has in the past had a material negative impact on our reported results. This risk could have a material adverse effect on our business financial condition, cash flow and results of operations in the future.

        Our policy is to convert into pounds sterling all revenues arising in currencies other than US dollars together with sufficient US dollar revenues to fund the remaining pounds sterling expenses. Outside the United Kingdom, only those cash flows necessary to fund mismatches between revenues and expenses are converted into local currency; amounts remitted to the United Kingdom are generally converted into pounds sterling. These transactional currency exposures are generally managed by entering into forward exchange contracts. It is our policy to hedge at least 25% of the next 12 months' exposure in significant currencies. We generally do not hedge exposures beyond three years.

Item 2—Properties

        We own and lease a number of properties for use as offices throughout the world and believe that our properties are generally suitable and adequate for the purposes for which they are used. The principal properties are located in the United Kingdom and the United States. Our principal office at Ten Trinity Square in London is a landmark building which we own.

Item 3—Legal Proceedings

        General.    We are subject to various actual and potential claims, lawsuits and proceedings relating principally to alleged errors and omissions in connection with the placement of insurance and reinsurance in the ordinary course of business. Similar to other corporations, we are also subject to a variety of other claims, including those relating to our employment practices. Some of those claims, lawsuits and proceedings seek damages in amounts which could, if assessed, be significant. Most of the claims, lawsuits and proceedings arising in the ordinary course of business are covered by professional indemnity or other appropriate insurance. In respect of self-insured deductibles, we have established provisions against these items which are believed to be adequate in the light of current information and legal advice, and we adjust such provisions from time to time according to developments. On the basis of current information, we do not expect that the outcome of the actual claims, lawsuits and proceedings to which we are subject or potential claims, lawsuits and proceedings of which we are aware, including those discussed below, either individually or in the aggregate, will have a material adverse effect on our financial condition, results of operations or liquidity.

        The most significant actual or potential claims, lawsuits and proceedings of which we are currently aware are:

        Sovereign/WFUM.    Sovereign, a wholly owned subsidiary of ours, operated as an insurance company in the United Kingdom and from 1972 Sovereign's underwriting activities were managed by

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another wholly owned subsidiary of ours, Willis Faber (Underwriting Management) Limited, or WFUM. WFUM also provided underwriting agency and other services to third-party insurance companies, which we refer to as the stamp companies, some of which are long-standing clients of ours. As an underwriting agent, WFUM did not issue any contracts of insurance or reinsurance in its own name or retain any underwriting risks for its own account. As part of its services as agent, WFUM arranged insurance and reinsurance business on behalf of Sovereign and the stamp companies in the following main classes of insurance: marine, non-marine, casualty and aviation. WFUM also arranged reinsurance on behalf of Sovereign and the stamp companies through third-party brokers, as well as through brokers within our group of companies.

        In 1991, Sovereign ceased underwriting new business and WFUM ceased arranging new business on behalf of Sovereign and the stamp companies. From that time until August 1998, WFUM administered the business it arranged on behalf of Sovereign and the stamp companies, referred to as handling the "run-off" of the business. From 1998, the run-off services were transferred to a new subsidiary of ours which services have in turn been sub-contracted to a third party with experience in running off pools with an insolvent member. In the case of Sovereign, those services are provided directly by that third party. One of our subsidiaries agreed with certain of the stamp companies to fund certain costs of the run-off, subject to certain agreed guidelines as to timing and amount. The amounts to be funded under the run-off arrangements are currently under review with the stamp companies. Although we expect the run-off of the business to be conducted in an orderly manner, it may ultimately prove to be a lengthy and expensive process.

        In July 1997, Sovereign received an adverse arbitration decision in respect of a dispute between Sovereign and one of its reinsurers regarding the enforceability of certain reinsurance which WFUM had arranged. The award is confidential and non-binding as to third parties. As a result of the decision, the directors of Sovereign determined that Sovereign could not continue to trade unless Willis Group provided unlimited financial support. Willis Group's directors decided that, in the interests of our shareholders, this support for Sovereign could not be justified. Accordingly, Sovereign's directors placed Sovereign into provisional liquidation on July 11, 1997. On January 5, 2000, a scheme of arrangement proposed by Sovereign to its creditors became effective. The stated purpose of the scheme of arrangement is to resolve Sovereign's liabilities and provide that Sovereign's business is run off in as orderly a manner as possible. Sovereign's provisional liquidators have been discharged from office and have been appointed as scheme administrators. The scheme administrators have announced payments to creditors at a payment percentage rate of 35% payable out of Sovereign's assets. Those creditors with established scheme liabilities received payment by May 2001. Sovereign's assets are separate and distinct from ours, and any payment from Sovereign will have no effect on our results of operations, financial condition or liquidity.

        Following the adverse arbitration decision, Sovereign and certain of the stamp companies expressed concern about the enforceability of other reinsurance put in place by WFUM on behalf of Sovereign and the stamp companies. We understand Sovereign has prevailed in an arbitration to ensure that a reinsurer honors its obligations to Sovereign on similar facts to the previous adverse arbitration decision. We also understand that Sovereign and possibly some of the stamp companies have commenced arbitration proceedings with a number of other reinsurers that are at a preliminary stage. Accordingly, we cannot assure you that there will be no further arbitration decisions, court decisions or discounted settlements arising in the future that result in shortfalls in reinsurance recoveries for Sovereign or the stamp companies. Other reinsurers which underwrite Sovereign's or the stamp companies' reinsurance contracts may seek to challenge the enforceability of such contracts. The failure of Sovereign or the stamp companies to collect reinsurance following any adverse arbitration awards would increase the likelihood of them pursuing claims against WFUM.

        Sovereign and the stamp companies have reserved their rights generally in respect of such potential claims, and WFUM, Willis Group and certain of our brokerage subsidiaries have entered into

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standstill agreements which preserve the rights of potential claimants with respect to their potential claims. The scheme administrators and/or the stamp companies may seek to bring claims directly against Willis Group and hold it responsible for the liabilities of its subsidiaries. Although claims that Willis Group is liable merely because it is the subsidiary's parent are difficult to pursue successfully under English law, we cannot assure you that claims will not be made or, if made, that such claims could not succeed. The scheme administrators or the stamp companies may also seek to bring claims in respect of alleged acts or omissions of other subsidiaries or of Willis Group. Those companies in our group with insurance protection have therefore notified their insurance providers of certain potential claims.

        World Trade Center.    We acted as the insurance broker, but not as an underwriter, for the placement of both property and casualty insurance for a number of entities which were directly impacted by the September 11, 2001 destruction of the World Trade Center complex, including Silverstein Properties LLC, which acquired a 99-year leasehold interest in the twin towers and related facilities from the Port Authority of New York and New Jersey in July 2001. Although the World Trade Center complex insurance was bound at or before the July 2001 closing of the leasehold acquisition, consistent with standard industry practice, the final policy wording for the placements was still in the process of being finalized when the twin towers and other buildings in the complex were destroyed on September 11, 2001. There are a number of lawsuits pending in the United States between the insured parties and the insurers for several placements, including the Silverstein property placement, but we are not a party to any of these lawsuits. The principal issue in dispute in the Silverstein property litigation is whether the September 11 events constituted one or more occurrences for the purposes of the relevant insurance policies, and the outcome of this issue will significantly impact the amount that the insurers ultimately pay on the property policies. Other disputes may also arise in respect of the World Trade Center insurance placed by us which could affect the Company, including claims by one or more of the insureds that we made culpable errors or omissions in connection with our brokerage activities. However, we do not believe that our role as broker will lead to liabilities which in the aggregate would have a material adverse effect on our results of operations, financial condition or liquidity.

        Insurance Market Dispute.    Various legal proceedings are pending, have been concluded or may commence between reinsurers, reinsureds and in some cases their intermediaries, including reinsurance brokers, relating to personal accident excess of loss reinsurance for the years 1993 to 1998. The proceedings principally concern allegations by reinsurers that they have sustained substantial losses due to an alleged abnormal "spiral" in the market in which the reinsurance contracts were placed, the existence and nature of which, as well as other information, was not disclosed to them by the reinsureds or their reinsurance broker. A "spiral" is a market term for a situation in which reinsureds and reinsurers reinsure each other with the effect that the same loss or portion of that loss moves through the market multiple times.

        The reinsurers concerned have taken the position that, despite their decisions to underwrite risks or a group of risks, they are no longer bound by their reinsurance contracts. As a result, they have stopped settling claims and are seeking to recover claims already paid. We also understand that there have been two arbitration awards in relation to a spiral, among other things, in which the reinsurer successfully argued that it was no longer bound by parts of its reinsurance program. Willis Limited, our principal insurance brokerage subsidiary in the United Kingdom, acted as the reinsurance broker or otherwise as intermediary, but not as an underwriter, for numerous personal accident reinsurance contracts, including for two contracts that were involved in one of the arbitrations. Due to the small number of reinsurance brokers generally, Willis Limited was one of a small number of brokers active in the market for this reinsurance during the relevant period. We also utilized other brokers active in this market as sub-agents, including brokers who are parties to the legal proceedings described above, for certain contracts and may be responsible for any errors and omissions they may have made. A proceeding brought by one of the reinsurers in the English High Court against certain parties, including

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a sub-broker that Willis Limited used to place two of the contracts involved in this trial, has resulted in a favorable decision for the reinsurers. Although neither we nor any of our subsidiaries were a party to this or any other proceeding or arbitration, Willis Limited has entered into standstill agreements with certain of the principals to the reinsurance contracts placed at Willis Limited tolling the statute of limitations pending the outcome of proceedings between the reinsureds and reinsurers so that those reinsureds would not feel compelled to commence proceedings against Willis Limited in order to avoid the lapse of any claims they may have.

        Although at this time no claims are pending against Willis Limited and we have not joined any settlement effort, claims may be made against Willis Limited if reinsurers do not pay claims on policies issued by them. It is too early to know what amount of underwriting losses will be alleged to be attributable to an abnormal spiral or the other issues that may be raised, or what amount, if any, reinsureds or reinsurers or other intermediaries may seek to recover from Willis Limited.

        Baccala and Shoop.    Prior to 1984, Baccala and Shoop Insurance Services, a US subsidiary, acted as managing general agent for certain insurance issuing companies, including three subsidiaries of The Hartford Financial Services Group, Inc. Since Baccala and Shoop ceased active operations in 1983, issuing companies (including Hartford) have notified Baccala and Shoop of potential errors and omissions claims against Baccala and Shoop. In August 1987, Baccala and Shoop, Hartford and Willis North America Inc. entered into a Standstill Agreement, amended in 1994, pursuant to which the statutes of limitations on Hartford's claims against Baccala and Shoop were tolled indefinitely in exchange for Hartford's agreement to forbear filing complaints against Baccala and Shoop based on these potential claims. Hartford has not stated what it believes to be its total aggregate losses potentially attributable to Baccala and Shoop. Willis Group has established provisions in connection with Baccala and Shoop-related claims, and believes such provisions to be adequate.

Item 4—Submission of Matters to a Vote of Security Holders

        None.

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PART II

Item 5—Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities

Market Information

        Our Shares have been traded on the New York Stock Exchange under the symbol "WSH" since June 11, 2001. The high and low closing prices of our Shares, as reported by the New York Stock Exchange, are set forth below for the periods indicated.

        On February 27, 2004, the last reported sale price of our Shares as reported by the New York Stock Exchange was $38.35 per Share. As of February 27, 2004 there were approximately 675 shareholders of record of our Shares.

Dividends

        We normally pay dividends on a quarterly basis to shareholders of record on March 31, June 30, September 30 and December 31 with the first dividend paid on April 15, 2003 to shareholders of record on March 31, 2003. The dividend payment dates and amounts are as follows:

        On February 4, 2004 our Board of Directors increased the quarterly cash dividend to $0.1875 per Share, which will be payable on April 15, 2004 to shareholders of record on March 31, 2004.

        There are no governmental laws, decrees or regulations in Bermuda which will restrict the remittance of dividends or other payments to non-resident holders of the Company's common stock.

        On the date of this document there is no Bermuda income, corporation or profits tax, withholding tax, capital gains tax, capital transfer tax, estate duty or inheritance tax payable by us or our shareholders, other than shareholders ordinarily resident in Bermuda.

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        Pursuant to the Exempted Undertakings Tax Protection Act 1966, as amended, we have received an undertaking from the Bermuda Ministry of Finance, that, in the event of there being enacted in Bermuda any legislation imposing withholding or other tax computed on profits or income, or computed on any capital assets, gain or appreciation or any tax in the nature of estate duty or inheritance tax, such tax shall not until March 28, 2016 be applicable to us or to any of our operations, or to our Shares, debentures or other obligations except and so far as such tax applies to persons ordinarily resident in Bermuda and holding such shares, debentures or other obligations or any land leased or let to us in Bermuda.

        The gross amount of dividends paid to US shareholders will be treated as dividend income to such holders, to the extent paid out of current or accumulated earnings and profits, as determined under United States federal income tax principles. This income will be includable in the gross income of a US shareholder as ordinary income on the day received by the US shareholder. These dividends will not be eligible for the dividends received deduction allowed to corporations under the Internal Revenue Code of 1986, as amended.

        With respect to non-corporate US shareholders, certain dividends received before January 1, 2009 from a qualified foreign corporation may be subject to reduced rates of taxation. A foreign corporation is treated as a qualified foreign corporation with respect to dividends received from that corporation on shares that are readily tradable on an established securities market in the United States. United States Treasury Department guidance indicates that our Shares, which are listed on the New York Stock Exchange, are readily tradable on an established securities market in the United States. There can be no assurance that our Shares will be considered readily tradable on an established securities market in later years. Non-corporate US shareholders that do not meet a minimum holding period requirement for our Shares during which they are not protected from the risk of loss or that elect to treat the dividend income as "investment income" pursuant to section 163(d)(4) of the Code will not be eligible for the reduced rates of taxation regardless of our status as a qualified foreign corporation. In addition, the rate reduction will not apply to dividends if the recipient of a dividend is obligated to make related payments with respect to positions in substantially similar or related property. This disallowance applies even if the minimum holding period has been met. Non-corporate US shareholders should consult their own tax advisors regarding the application of these rules given their particular circumstances.

        To the extent that the amount of any distribution exceeds our current and accumulated earnings and profits for a taxable year, the distribution will first be treated as a tax-free return of capital, causing a reduction in the adjusted basis of the Shares. This will increase the amount of gain, or decrease the amount of loss, to be recognized by the US shareholder on a subsequent disposition of the Shares, and the balance in excess of adjusted basis will be taxed as capital gain recognized on a sale or exchange.

Securities Authorized for Issuance Under Equity Compensation Plans

        Information on our equity compensation plans is incorporated herein by reference to the material under the heading "Executive Compensation—Retirement and other Benefit Plans" from the 2004 Proxy Statement.

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Information Concerning Equity Compensation Plans

Sales of Unregistered Securities

        None.

Item 6—Selected Financial Data

Selected Historical Consolidated Financial Data

        The selected consolidated financial data presented below should be read in conjunction with the audited consolidated financial statements of the Company and the related notes and "Management's Discussion and Analysis of Financial Condition and Results of Operations" included elsewhere in this report.

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        The selected historical financial data presented below as of and for each of the five years ended December 31, 2003 have been derived from the audited consolidated financial statements of the Company, which have been prepared in accordance with US GAAP.