UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 11-K

(Mark One)

x                                   Annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934 for the fiscal year ended December 31, 2010

OR

o                                      Transition report pursuant to Section 15(d) of the Securities Exchange Act of 1934 for the transition period from         to        

Commission file number 1-8993

A.                                   Full title of the plan and the address of the plan, if different from that of the issuer named below:

ESURANCE INSURANCE SERVICES, INC. 401(K) PLAN

Esurance Insurance Services, Inc.

650 Davis Street

San Francisco, CA 94111

B.                                     Name of issuer of the securities held pursuant to the plan and the address of its principal executive office:

WHITE MOUNTAINS INSURANCE GROUP, LTD.

80 South Main Street

Hanover, New Hampshire 03755

REQUIRED INFORMATION

The following Financial Statements and Schedule for the Plan and a Written Consent of Independent Registered Public Accounting Firm are filed with, and included in, this Report as Exhibits 99(a) and 99(b) hereto, respectively, as detailed below:

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SIGNATURES

The Plan. Pursuant to the requirements of the Securities Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned, thereunto duly authorized.

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EXHIBIT INDEX

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Exhibit 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in the Registration Statement on Form S-8 (No. 333-132388) of White Mountains Insurance Group, Ltd. of our report dated June 28, 2011 with respect to the statements of net assets available for benefits of the Esurance Insurance Services, Inc. 401(k) Plan as of December 31, 2010 and 2009, the related statements of changes in net assets available for benefits for the years then ended, and the related supplemental schedule as of December 31, 2010, which report appears in the December 31, 2010 annual report on Form 11-K of the Esurance Insurance Services, Inc. 401(k) Plan.

MOHLER, NIXON & WILLIAMS

Accountancy Corporation

Campbell, California

June 28, 2011

Exhibit 99(a)

Esurance Insurance Services, Inc.

401(k) Plan

Financial Statements

December 31, 2010 and 2009

ESURANCE INSURANCE SERVICES, INC.

401(k) PLAN

Financial Statements and Supplemental Schedule

December 31, 2010 and 2009

Table of Contents

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Participants and

Plan Administrator of the

Esurance Insurance Services, Inc.

401(k) Plan

We have audited the financial statements of the Esurance Insurance Services, Inc. 401(k) Plan (the Plan) as of December 31, 2010 and 2009, and for the years then ended, as listed in the accompanying table of contents.  These financial statements are the responsibility of the Plan’s management.  Our responsibility is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with standards of the Public Company Accounting Oversight Board (United States).  Those standards require that we plan and perform the audits to obtain reasonable assurance about whether the financial statements are free of material misstatement.  We were not engaged to perform an audit of the Plan’s internal control over financial reporting.  Our audits included consideration over financial reporting as a basis for designing audit procedures that are appropriate in the circumstances, but not for the purpose of expressing an opinion on the effectiveness of the Plan’s internal control over financial reporting.  Accordingly, we express no such opinion.  An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements.  An audit also includes assessing the accounting principles used and significant estimates made by the Plan’s management, as well as evaluating the overall financial statement presentation.  We believe that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in all material respects, the net assets available for benefits of the Plan as of December 31, 2010 and 2009, and the changes in net assets available for benefits for the years then ended, in conformity with accounting principles generally accepted in the United States of America.

Our audits were performed for the purpose of forming an opinion on the basic financial statements taken as a whole.  The supplemental schedule, as listed in the accompanying table of contents, is presented for the purpose of additional analysis and is not a required part of the basic financial statements but is supplementary information required by the Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974.  This supplemental schedule is the responsibility of the Plan’s management.  The supplemental schedule has been subjected to the auditing procedures applied in the audits of the basic financial statements and, in our opinion, is fairly stated in all material respects in relation to the basic financial statements taken as a whole.

MOHLER, NIXON & WILLIAMS

Accountancy Corporation

Campbell, California

June 28, 2011

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ESURANCE INSURANCE SERVICES, INC.

401(k) PLAN

STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS

See notes to financial statements.

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ESURANCE INSURANCE SERVICES, INC.

401(k) PLAN

STATEMENTS OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS

See notes to financial statements.

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ESURANCE INSURANCE SERVICES, INC.

401(k) PLAN

NOTES TO FINANCIAL STATEMENTS

DECEMBER 31, 2010 AND 2009

NOTE 1 - THE PLAN AND ITS SIGNIFICANT ACCOUNTING POLICIES

General - The following description of the Esurance Insurance Services, Inc. 401(k) Plan (the Plan) provides only general information. Participants should refer to the Plan document for a more complete description of the Plan’s provisions.

The Plan is a defined contribution plan that was established in 2000 by Esurance Inc. to provide benefits to eligible employees, as defined in the Plan document.  On December 31, 2009 Esurance Inc. changed its name to Esurance Insurance Services, Inc. (the Company), and the Plan was accordingly renamed the Esurance Insurance Services, Inc. 401(k) Plan effective January 1, 2010.  The Company is a wholly-owned subsidiary of White Mountains Insurance Group, Ltd. (the Parent).

On June 14, 2010 the Plan was amended and restated effective as of January 1, 2010 to include a few minor revisions to the provisions for plan transfers and profit sharing.  These amendments had no material impact on the Plan participants.  On December 20, 2010 the Plan was amended again to incorporate the Heroes Earnings Assistance and Relief Tax Act of 2008 and the Worker, Retiree, and Employer Recovery Act of 2008, which had no affect on the Plan participants.

The Plan is currently designed to be qualified under the applicable requirements of the Internal Revenue Code, as amended, and the provisions of the Employee Retirement Income Security Act of 1974 (ERISA), as amended.

Administration - The Company has appointed an Administrative Committee (the Committee) to manage the operation and administration of the Plan.  The Company has contracted with MG Trust Company (MG Trust), also known as Matrix Capital Bank, to act as custodian and with Digital Retirement Solutions, Inc. (DRS) to act as the third-party administrator to process and maintain the records of participant data.  Substantially all expenses arising from MG Trust and DRS are paid by the Plan; other costs incurred for administering the Plan, such as audit fees and Company personnel, are paid by the Company.

Estimates - The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and changes therein, and disclosure of contingent assets and liabilities.  Actual results could differ from those estimates.

Basis of accounting - The financial statements of the Plan are prepared on the accrual method of accounting in accordance with GAAP.

Forfeited accounts — Forfeited nonvested accounts are used to pay Plan expenses or to reduce future employer contributions. The following represents forfeitures and their application to Plan expenses:

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Investments - Investments of the Plan are held by MG Trust and invested based solely upon instructions received from participants.  The Plan investments include the following:

·                  Various mutual funds that are actively traded on public stock exchanges at quoted market prices;

·                  The White Mountains Insurance Unitized Stock Fund (Parent company stock) which comprises common shares of the Parent that are also traded on a public stock exchange at quoted market prices, plus some amount of non-interest-bearing cash.  The carrying value of this Fund is exactly equal to the sum of the market value of the shares held plus the face value of the cash.

·                  Wells Fargo Stable Value Fund (a common/collective trust) that is traded over-the-counter at quoted market prices.  This fund invests 100% in a Wells Fargo Stable Return Fund, which in turn holds (a) investment contracts issued by a financial institution to provide a stated rate of return for a specified period of time, and (b) security-backed contracts comprising fixed-income securities and contract value guarantees (wrappers) provided by an outside party.  Wrappers provide contract value payments for certain participant-initiated withdrawals and transfers, a floor crediting rate, and return of fully accrued contract value at maturity.

Wells Fargo reserves the right to require a twelve-month notice for withdrawal of assets from the Wells Fargo Stable Value Fund initiated by the Plan sponsor.

There are several risks specific to investment contracts.  One of the primary risks involved is credit risk of the contract issuer.  Credit risk for security-backed contracts includes risks arising from potential inability of the issuer to meet the terms of the contract wrapper and the potential default of the underlying fixed-income securities.  Also, liquidity is limited because of the unique characteristics of investment contracts and the absence of an actively traded secondary market.  Interest rate risk may also arise because rates may be fixed with these products.

The Wells Fargo Stable Value Fund is considered a fully-benefit-responsive contract.  Although all investment contracts held by a defined contribution plan are required to be reported at fair value, an adjustment from fair value to contract value is presented for fully-benefit-responsive contracts because contract value reflects the amount participants would receive if they were to initiate permitted transactions under the terms of the Plan.  The statements of changes in net assets available report changes in fully-benefit-responsive contracts at contract value.

Notes receivable from participants - Reported at remaining unpaid principal and accrued but unpaid interest as of the reporting date, consistent with the Accounting Standards Update (ASU) 2010-25 described in the “recent accounting pronouncements” section below.  Delinquent participant loans are reclassified as distributions based upon the terms of the Plan document.

Income recognition - Purchases and sales of investment assets are recorded on a trade-date basis.  Interest income is recognized on an accrual basis and dividends are recorded on the ex-dividend date.  Net appreciation (depreciation) summarizes the Plan’s gains (losses) on investments sold during the year or held at year end.

Income taxes - The Plan has adopted a prototype plan that has received an opinion letter from the Internal Revenue Service.  The Company believes that the Plan is operated in accordance with, and qualifies under, the applicable requirements of the Internal Revenue Code and related state statutes, and that the trust, which forms a part of the Plan, is exempt from federal income and state franchise taxes.

GAAP requires plan management to evaluate tax positions taken by the plan and recognize a tax liability (or asset) if the plan has taken an uncertain position that more likely than not would not be sustained upon examination by the Internal Revenue Service.  No uncertain positions have been identified that would require recognition of a liability (or asset) or disclosure in the financial statements as of December 31, 2010.  The Plan is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress.  The Plan administrator believes the Plan is no longer subject to income tax examinations for years prior to 2007.

Risks and uncertainties - The Plan provides for various investment options in any combination of investment securities offered by the Plan.  Investment securities are exposed to various risks, such as interest rate, market fluctuations and credit risks.  Due to the risk associated with certain investment securities, it is at least reasonably possible that changes in market values, interest rates or other factors in the near term would materially affect participants’ account balances and the amounts reported in the statements of net assets available for benefits and the statements of changes in net assets available for benefits.

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Recent accounting pronouncements — In January 2010, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2010-06, Fair Value Measurements and Disclosures (Topic 820): Improving Disclosures about Fair Value Measurements, which expanded the required disclosures about fair value measurements.  In particular, this guidance requires information about purchases, sales, issuances and settlements to be presented separately in the reconciliation for level 3 fair value measurements.  This guidance is effective for annual reporting periods beginning after December 15, 2010.  The Company is currently evaluating the impact that this guidance will have on the Plan’s financial statement disclosures.

In September 2010, the FASB issued ASU 2010-25, Plan Accounting-Defined Contribution Pension Plans (Topic 962), Reporting Loans to Participants by Defined Contribution Pension Plans.  The guidance requires Plan participant loans be classified as notes receivable from participants, which are segregated from plan investments and measured at their unpaid principal balance plus any accrued but unpaid interest.  This guidance must be applied retrospectively to all prior periods presented, effective for fiscal years ending after December 15, 2010.  The Plan adopted the amendment for the year ended December 31, 2010 and has restated the financial statements for 2009 to reflect the retrospective application.  There was no impact to the net assets as of December 31, 2010 and 2009 as a result of the adoption.

NOTE 2 - FAIR VALUE MEASUREMENTS

Fair value is the price that would be received to sell an asset in an orderly transaction between market participants at the measurement date.  GAAP provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value.  The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets (level 1 measurements) and the lowest priority to unobservable inputs (level 3 measurements).  The three levels of the fair value hierarchy under GAAP are described below:

Level 1 -                     Inputs to the valuation methodology are unadjusted quoted prices for identical assets in active markets that the Plan has the ability to access.

Level 2 -                     Inputs to the valuation methodology include:

·                  Quoted market prices for similar assets in active markets;

·                  Quoted prices for identical or similar assets in inactive markets;

·                  Inputs other than quoted prices that are observable for the asset;

·                  Inputs that are derived principally from or corroborated by observable market   data by correlation or other means.

If the asset has a specified (contractual) term, the level 2 input must be observable for substantially the full term of the asset.

Level 3 -                Inputs to the valuation methodology are unobservable and significant to the fair value measurement.

The asset’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.  Valuation techniques used need to maximize the use of observable inputs and minimize the use of unobservable inputs.

The methods described in Note 1 may produce an estimate of fair value that may not be indicative of net realizable value or reflective of future fair values.  Furthermore, while the Plan believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

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The White Mountains Insurance Unitized Stock Fund, and other mutual funds are valued based on the closing quoted stock exchange price, and the Wells Fargo Stable Value Fund is valued based on the closing quoted over-the-counter price as of the reporting date.  The following table sets forth by level, within the fair value hierarchy, the Plan’s assets at fair value as of December 31:

No assets were transferred between level 1, level 2 or level 3 in either year.

NOTE 3 - RELATED PARTY TRANSACTIONS

Aggregate investment in Parent company common stock at December 31, 2010 and 2009 was as follows:

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NOTE 4 - PARTICIPATION AND BENEFITS

Participant contributions - Participants may elect to have the Company contribute their eligible pre-tax or Roth after-tax compensation to the Plan up to the amount allowable under the Plan document and current income tax regulations.  Participants who elect to have the Company contribute a portion of their compensation to the Plan agree to accept an equivalent reduction in taxable compensation.  Contributions withheld are invested in accordance with the participant’s direction.  If a participant does not make an election to contribute pre-tax compensation or waive contribution, there is a Plan provision for automatic enrollment into a moderate risk portfolio at a 3% contribution level.

Participants are also allowed to make rollover contributions of amounts received from other tax-qualified employer-sponsored retirement plans.  Such contributions are deposited in the appropriate investment funds in accordance with the participant’s direction and the Plan’s provisions.

Employer contributions - The Company is allowed to make discretionary matching (and in 2009 only, profit sharing) contributions as defined in the Plan and as approved by the Board of Directors.  During 2010 and 2009, the Company matched 50% of participant’s deferrals up to 6% of eligible compensation.  No discretionary profit sharing contribution was made for the year ended December 31, 2009.

Vesting - Participants are immediately vested in their contributions.  Participants are fully (cliff) vested in the employer’s discretionary matching and profit sharing contributions allocated to their account after three years of credited service.

Participant accounts - Each participant’s account is credited with the participant’s contribution, Plan earnings or losses and an allocation of the Company’s contributions, if any.  Allocations of the Company’s contributions are based on participant contributions or eligible compensation, as defined in the Plan.

Payment of benefits - Upon termination, the participants or beneficiaries may elect to leave their account balance in the Plan, or receive their total benefits in a lump sum.  The Plan does not allow for automatic lump sum distribution or automatic IRA rollover of participant vested account balances.

Notes receivable from participants - The Plan allows participants to borrow not less than $1,000 and up to the lesser of $50,000 or 50% of their vested account balance.  The loans are secured by the participant’s vested balance.  Such loans bear interest at the available market financing rates and must be repaid to the Plan within a five-year period, unless the loan is used for the purchase of a principal residence in which case the maximum repayment period is up to 30 years.  The specific terms and conditions of such loans are established by the Committee.  Outstanding loans at December 31, 2010 carry interest rates ranging from 5.25% to 10.25%.

The following is a reconciliation of beginning and ending balances for Plan participant loans during the year ended December 31:

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NOTE 5 - INVESTMENTS

The following table presents the assets representing 5% or more of the Plan’s net assets available for benefits in either year as of December 31:

The Plan’s investments appreciated in value as follows for the years ended December 31:

NOTE 6 - RECONCILIATION OF FINANCIAL STATEMENTS TO FORM 5500

The following is a reconciliation of net assets available for benefits per the financial statements to Form 5500 as of December 31:

The following is a reconciliation of the affected components of the changes in net assets available for benefits per the financial statements to Form 5500 for the years ended December 31:

NOTE 7 - PLAN TERMINATION OR MODIFICATION

The Company intends to continue the Plan indefinitely for the benefit of its participants; however, it reserves the right to terminate or modify the Plan at any time by resolution of its Board of Directors and subject to the provisions of ERISA.  In the event the Plan is terminated in the future, participants would become fully vested in their accounts.

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NOTE 8 — SUBSEQUENT EVENTS

In February 2011 the Company replaced DRS with the Newport Group as the third-party administrator to the Plan; the Company does not expect the change to materially affect the Plan.

On May 17, 2011 the Parent entered into an agreement to sell the Company to Allstate Insurance Company, subject to the approval of various state insurance regulators.  The sale is expected to be completed during the third quarter of 2011, and the impact of the sale on the Plan is not determinable at this time.

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SUPPLEMENTAL SCHEDULE

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SCHEDULE H, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

DECEMBER 31, 2010

* Party-in-interest

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