EXHIBIT 99(v)


     NOTE PURCHASE OPTION AGREEMENT, dated as of June 1, 2001 (this
"Agreement"), among CGU International Holdings Luxembourg S.A., a Luxembourg
corporation, CGU Holdings LLC, a Delaware limited liability company (each a
"Noteholder," which term shall include any person who becomes a Noteholder in
accordance with Section 4.2 hereof) and White Mountains Insurance Group, Ltd., a
company existing under the laws of Bermuda (the "Optionee").

     WHEREAS, pursuant to a Stock Purchase Agreement dated as of September 24,
2000 by and among CGU International Holdings Luxembourg S.A., CGU Holdings LLC
(each a "Seller"), CGNU plc, the Optionee, TACK Holding Corp. (the "Note
Issuer") and TACK Acquisition Corp., as amended by Amendment No. 1 thereto dated
as of October 15, 2000 and by Amendment No. 2 thereto dated as of February 20,
2001 (as amended, the "Stock Purchase Agreement"), the Note Issuer issued to the
Sellers subordinated promissory notes due November 29, 2002 (the "Maturity
Date") (such promissory notes and any other like promissory note that may be
issued by the Note Issuer in replacement or upon transfer (whether in whole or
in part) of any of them, or of any such other promissory note, and that shall be
outstanding are each referred to herein as a "Note") in the aggregate principal
amount of $260,000,000.00;

     WHEREAS, Exhibit G to the Stock Purchase Agreement contemplates that each
of the Sellers would grant the Optionee an option to purchase the Notes issued
to such Seller from such Seller (or any person to whom such Seller or any
transferee of such Seller may transfer such Note) on the terms and subject to
the conditions set forth in such Exhibit G; and

     WHEREAS, in accordance with their respective obligations undertaken in the
Stock Purchase Agreement, including Exhibit G thereto, each Seller desires to
grant to the Optionee, and the Optionee desires to accept from each Seller, an
option to purchase such Seller's Note on the terms and subject to the conditions
set forth herein;

     NOW, THEREFORE, in consideration of the covenants and agreements contained
in this Agreement, the parties hereto agree as follows:


                                    ARTICLE I
                                   THE OPTION

     SECTION 1.1 OBLIGATION TO SELL. On the terms and subject to the conditions
of this Agreement, each Noteholder hereby grants the Optionee an option to
purchase the Notes held by such Noteholder. On the Maturity Date, if the
Optionee shall have delivered an Exercise Notice (as defined below) to the
Noteholders in accordance with Section 1.2 hereof, then subject to satisfaction
of the conditions set forth in Article III hereof, each Noteholder shall sell to
the Optionee, and the Optionee shall purchase from each Noteholder, for the
consideration specified in Section 1.3 hereof, the Notes held by such Noteholder
specified in such Exercise Notice or such lesser portion thereof as may be
determined pursuant to Section 1.5 hereof.

     SECTION 1.2 EXERCISE NOTICE. If the Optionee desires to purchase the Notes
as provided in this Agreement, the Optionee shall deliver to each Noteholder a
notice (the "Exercise







Notice") not less than 10 days before the Maturity Date and not more than 90
days before the Maturity Date, specifying (i) that the Optionee has elected to
purchase the Notes in accordance with this Agreement and (ii) the amount of
consideration that is payable by the Optionee.

     SECTION 1.3 CONSIDERATION. The consideration payable by the Optionee upon
purchase of any Note shall consist of a number of common shares of the Optionee
("Common Shares") equal to the Number of Shares Issuable (as defined below).
Such Common Shares when issued shall be validly issued, fully paid and
non-assessable and free and clear of all liens. The "Number of Shares Issuable"
shall be a number (rounded to the nearest whole number) determined by dividing
the principal amount of the Note to be purchased, plus accrued and unpaid
interest thereon calculated in accordance with the provisions of the Notes, by
the Per Share Price as of the Maturity Date; PROVIDED, HOWEVER, that any
calculation of Number of Shares Issuable shall be made without any reduction for
any and all present or future taxes, levies, imposts, deductions, charges or
withholdings, and all liabilities with respect thereto. The "Per Share Price"
initially shall be $245 per share, subject to adjustment pursuant to Article II
hereof.

     SECTION 1.4 PARTIAL PURCHASES PRO RATA; NO RIGHT OF SET-OFF.

     (a) Except as may be required or permitted by Section 1.5 hereof or as
may be agreed by the Optionee and any Noteholder with respect to such
Noteholder's Notes, the Optionee must purchase the same proportion of Notes
from each Noteholder if it elects to purchase any Notes hereunder.

     (b) Without the prior written consent of a Noteholder, the Optionee shall
not be entitled to set-off its obligation to pay the consideration payable by it
to such Noteholder in accordance with Section 1.3 hereof against any amount that
such Noteholder may owe or be alleged to owe the Optionee.

     SECTION 1.5 LIMITATION ON AMOUNT OF NOTES TO BE PURCHASED.

     (a) Notwithstanding anything in this Agreement to the contrary, the
Optionee shall not be permitted to purchase from any Noteholder or group of
Noteholders ("Control Noteholders") an aggregate principal amount of Notes
that is greater than the aggregate principal amount (the "Note Limit") that
would require the Optionee to deliver to such Control Noteholders, in
consideration for their Notes (including accrued and unpaid interest thereon
in accordance with Section 1.3), an aggregate number of Common Shares equal
to the Share Limit. The "Share Limit" means the greatest number of Common
Shares that could as of the Maturity Date be acquired by such Control
Noteholders without any of them or any parent company thereof being required
to file a "Form A" or other request for approval of the acquisition by such
Noteholder or parent company of control of any direct or indirect insurance
company subsidiary of Optionee with any U.S. insurance regulator. If,
pursuant to the first sentence of this Section 1.5(a), the Optionee is not
permitted to purchase the full aggregate principal amount of the Notes held
by Control Noteholders sought to be purchased by the Optionee, the Optionee
shall purchase from such Control Noteholders an aggregate principal amount of
Notes equal to the Note Limit, with the amount to be purchased allocated
among such Control Noteholders as they shall direct in a notice delivered to
the Optionee at least three business days prior to the Maturity Date (or, if
no such notice is delivered, pro rata according to the principal amount of
Notes held by them). Any partial purchase pursuant to this Section 1.5 shall
not affect the rights of any Noteholder to

                                       -2-





receive repayment from the Note Issuer of the principal and accrued interest on
such Noteholder's Notes that are not purchased by the Optionee.

     (b) If requested by the Optionee in the Exercise Notice, each Noteholder
shall use its commercially reasonable efforts prior to the Maturity Date to file
and seek and to cause its affiliates to file and seek approval of a disclaimer
of control or other exemptive relief from the appropriate insurance regulators
permitting the Optionee to purchase all of the Notes held by such Noteholder in
exchange for Common Shares without such Noteholder or any affiliate being
required to file a request for approval of acquisition of control as described
in Section 1.5(a). Any such approval that may be in effect as of the Maturity
Date shall be taken into consideration in determining the Share Limit with
respect to such Noteholder or group of Noteholders; PROVIDED that any such
approval shall not be considered for the foregoing purpose if it contains any
materially adverse condition, restriction or requirement (not including any such
condition, restriction or requirement customarily imposed by the issuing
insurance regulator in connection with similar transactions).

     SECTION 1.6 CLOSING. If the Optionee has validly delivered an Exercise
Notice, then on the terms and subject to the conditions of this Agreement, the
closing of the purchase and sale of the Notes (the "Closing") shall be held at
9:00 a.m. (New York City time) on the Maturity Date at the offices of LeBoeuf,
Lamb, Greene & MacRae, L.L.P., 125 West 55th Street, New York, New York 10019.
At the Closing, (i) each Noteholder shall deliver to the Optionee a Note,
registered in the name of the Optionee, in the principal amount equal to the
aggregate principal amount of the Notes to be purchased by the Optionee from
such Noteholder, (ii) the Optionee shall issue and deliver to each Noteholder a
certificate or certificates, registered in the name of such Noteholder,
representing such number of validly issued, fully paid and non- assessable
Common Shares, free and clear of all liens, as shall be issuable to such
Noteholder in accordance with Section 1.3 hereof, (iii) the Noteholders and the
Optionee shall deliver cross- receipts in appropriate form, (iv) the Optionee
shall be deemed to make to the Noteholder the representations, warranties,
covenants and agreements required by Sections 9(c), (d) and (e) of the Note and
(v) the Noteholders and the Optionee shall execute and deliver a registration
rights agreement substantially in the form of Exhibit 2 hereto.


                                   ARTICLE II
                                  ANTI-DILUTION

     SECTION 2.1 ADJUSTMENT OF PER SHARE PRICE; NUMBER OF SHARES ISSUABLE. The
Per Share Price shall be subject to adjustment from time to time from and after
the date of this Agreement through the Maturity Date in the applicable manner,
and upon the occurrence of any of the events, enumerated in this Section 2.1.

     (a) SHARE DIVIDENDS, SUBDIVISIONS, RECLASSIFICATIONS, COMBINATIONS. If the
Optionee declares a dividend or makes a distribution on its outstanding Common
Shares in Common Shares, or subdivides or reclassifies its outstanding Common
Shares into a greater number of Common Shares, or combines its outstanding
Common Shares into a smaller number of Common Shares, then, in each such event,

                                       -3-





          (i) the then applicable Per Share Price shall be adjusted so that the
     Noteholders shall be entitled to receive, upon the exercise by the Optionee
     of its option hereunder, the number of Common Shares which such Noteholder
     would have been entitled to receive immediately after the happening of any
     of the events described above had such option been exercised immediately
     prior to the happening of such event or the record date therefor, whichever
     is earlier; and

          (ii) an adjustment to the Per Share Price made pursuant to this clause
     (a) shall become effective (A) in the case of any such dividend or
     distribution, immediately after the close of business on the record date
     for the determination of holders of Common Shares entitled to receive such
     dividend or distribution or (B) in the case of any such subdivision,
     reclassification or combination, at the close of business on the day upon
     which such corporate action becomes effective.

     (b) ISSUANCE OF COMMON SHARES OR CONVERTIBLE SECURITIES.

          (i) If the Optionee issues or sells any Common Shares or Convertible
     Securities, other than any Permitted Issuance or issuance of Common Shares
     to which Section 2.1(a) or (c) applies, without consideration or at a price
     per Common Share (or having an exercise, exchange or conversion price per
     Common Share) less than the closing price per Common Share on the trading
     day immediately preceding (x) the Determination Date, if one exists in
     connection with such event, or (y) in all other cases, the date of such
     issuance, then in each such event, the Per Share Price shall be adjusted to
     equal the then applicable Per Share Price multiplied by a fraction, of
     which:

               (A) the numerator shall be the sum of (I) the number of Common
          Shares outstanding on such date and (II) the number of Common Shares
          which the aggregate consideration receivable by the Optionee for the
          total number of Common Shares so issued (or into which the Convertible
          Securities may be exercised, exchanged or converted) would purchase at
          the Fair Market Value on the date specified in clause (x) or (y)
          above, as applicable. For purposes of this subparagraph, the aggregate
          consideration receivable by the Optionee in connection with the
          issuance of Common Shares or of securities exercisable or exchangeable
          for or convertible into Common Shares shall be deemed to be equal to
          the sum of the net offering price (after deduction of any related
          expenses payable to third parties), if any, of all such securities
          plus the minimum aggregate amount, if any, payable upon exercise or
          conversion of any such Convertible Securities into Common Shares, and

               (B) the denominator shall the sum of (I) the number of Common
          Shares outstanding on such date and (II) the number of additional
          Common Shares issued (or into which the Convertible Securities may be
          exercised, exchanged or converted).


                                       -4-





          (ii) an adjustment to the Per Share Price made pursuant to this clause
     (b) shall become effective immediately after the Determination Date, if
     applicable, or if not applicable then the date of such issuance.

          (iii) upon the expiration or termination of any unexercised
     Convertible Securities or of conversion or exchange privileges pursuant to
     any Convertible Securities for which any adjustment to the Per Share Price
     was made pursuant to this clause (b), the then applicable Per Share Price
     shall be readjusted and shall thereafter be such number as would have been
     determined had the Per Share Price been originally adjusted (or had the
     original adjustment not been required, as the case may be) on the basis of
     (A) the Common Shares, if any, actually issued or sold upon the exercise of
     such Convertible Securities or conversion or exchange right of such
     Convertible Securities and (B) the consideration, if any, actually received
     by the Optionee upon such exercise or conversion plus the consideration, if
     any, actually received by the Optionee for the issuance or sale of all of
     such Convertible Securities whether or not exercised, converted or
     exchanged. No such readjustment shall have the effect of decreasing the Per
     Share Price by an amount in excess of the amount of the adjustment
     initially made for the issuance or sale of such Convertible Securities.

     (c) ISSUANCES UPON MERGER, CONSOLIDATION OR SALE OF OPTIONEE. If the
Optionee shall be a party to any transaction (including a merger, consolidation,
sale of all or substantially all of the Optionee's assets, liquidation or
recapitalization of the Common Shares and excluding any transaction to which
Section 2.1(a), (b) or (f) applies) in which the previously outstanding Common
Shares shall be changed into or, pursuant to the operation of law or the terms
of the transaction to which the Optionee is a party, exchanged for different
securities of the Optionee or common shares or other securities of another
corporation or interests in a noncorporate entity or other property (including
cash) or any combination of any of the foregoing, then the Noteholders shall be
entitled to receive, upon the exercise by the Optionee of its option hereunder,
the number of common shares or other securities of the Optionee or other
corporation or interests in a noncorporate entity or other property (including
cash) or any combination of the foregoing equal to (A) the aggregate amount of
stock, securities, cash and/or any other property (payable in kind), as
applicable, into which or for which each Common Share is changed or exchanged
multiplied by (B) the Number of Shares Issuable in effect immediately prior to
the consummation of such transaction. If any transaction described in this
Section 2.1(c) is effected and any stock, securities and/or other property
becomes deliverable upon exercise of the option hereunder the Optionee shall be
obligated to make future adjustments to the amount of stock, securities and/or
other property deliverable upon exercise of the option in the circumstances and
amounts set forth in this Section 2.1 as if such stock, securities and/or other
property were Common Shares.

     (d) DIVIDENDS OF CASH, SECURITIES, ASSETS. If the Optionee shall
distribute, by dividend or otherwise, to all holders of outstanding Common
Shares evidences of its indebtedness, shares of capital stock, cash or other
property or assets (but excluding any dividend or distribution paid exclusively
in cash and any dividend or distribution referred to in paragraphs (a) or (b) of
this Section), then, in each such event, the Per Share Price shall be adjusted
so that the same shall equal the price determined by multiplying the Per Share
Price in effect

                                       -5-





immediately prior to the close of business on the date fixed for the
determination of stockholders entitled to receive such dividend or distribution
by a fraction, of which the numerator shall be the Fair Market Value per Common
Share on the Determination Date less the then fair market value (as reasonably
determined in good faith by the Board of Directors of the Optionee, whose
determination shall be conclusive and described in a board resolution) of the
portion of the evidences of indebtedness, shares of capital stock, cash, or
other property or assets so distributed applicable to one Common Share and the
denominator shall be such Fair Market Value per Common Share, such adjustment to
become effective immediately prior to the opening of business on the
Determination Date.

     (e) CASH DIVIDENDS. In case the Optionee shall (I) by dividend or
otherwise, make a distribution to all holders of outstanding Common Shares
exclusively in cash (excluding any cash that is distributed as part of a
distribution referred to in paragraph (d) of this Section) in an aggregate
amount that, combined together with (II) the aggregate amount of any other
dividends to all holders of Common Shares made exclusively in cash within the 12
months preceding the date of payment of such distribution and in respect of
which no adjustment pursuant to this paragraph (e) or paragraph (f) of this
Section has been made and (III) the aggregate of any cash plus the fair market
value, as of the expiration of the applicable tender or exchange offer referred
to below (as reasonably determined in good faith by the Board of Directors,
whose determination shall be conclusive and described in a board resolution), of
consideration payable in respect of any tender or exchange offer (other than
consideration payable in respect of any odd-lot tender offer) by the Optionee or
any of its subsidiaries for all or any portion of the Common Shares concluded
within the 12 months preceding the date of payment of the distribution described
in clause (I) above and in respect of which no adjustment pursuant to this
paragraph (e) or paragraph (f) of this Section has been made, exceeds 10% of the
product of the Fair Market Value per Common Share on the Determination Date
times the number of Common Shares outstanding on such Determination Date (the
"Dividend Threshold"), then, and in each such case, immediately after the close
of business on such Determination Date, the Per Share Price shall be adjusted so
that the same shall equal the price determined by multiplying the Per Share
Price in effect immediately prior to the close of business on the date fixed for
determination of the stockholders entitled to receive such distribution by a
fraction (i) the numerator of which shall be equal to the Fair Market Value per
Common Share on the Determination Date less an amount equal to the quotient of
(x) the combined amount distributed or payable in the transactions described in
clauses (I), (II) and (III) above less the Dividend Threshold and (y) the number
of Common Shares outstanding on such Determination Date and (ii) the denominator
of which shall be equal to the Fair Market Value per Common Share on such
Determination Date.

     (f) TENDER OR EXCHANGE OFFERS. In case (I) a tender or exchange offer made
by the Optionee or any subsidiary of the Optionee for all or any portion of the
Common Shares is consummated and such tender or exchange offer (as amended upon
the expiration thereof) shall require the payment to stockholders (based on the
Common Shares accepted for payment in such tender or exchange offer) of an
aggregate consideration having a fair market value (as reasonably determined in
good faith by the Board of Directors, whose determination shall be conclusive
and described in a board resolution) at the last time (the "Expiration Time")
tenders or exchanges may be made pursuant to such tender or exchange offer (as
it may be amended) that, combined

                                       -6-





together with (II) the aggregate of the cash plus the fair market value (as
reasonably determined in good faith by the Board of Directors, whose
determination shall be conclusive and described in a board resolution), as of
the expiration of such tender or exchange offer, of consideration payable in
respect of any other tender or exchange offer (other than consideration payable
in respect of any odd-lot tender offer) by the Optionee or any subsidiary of the
Optionee for all or any portion of the outstanding Common Shares consummated
within the 12 months preceding the expiration of such tender or exchange offer
and in respect of which no adjustment pursuant to paragraph (e) of this Section
or this paragraph (f) has been made and (III) the aggregate amount of any
dividends to all holders of the Optionee's Common Shares made exclusively in
cash within the 12 months preceding the expiration of such tender or exchange
offer and in respect of which no adjustment pursuant to paragraph (e) of this
Section or this paragraph (f) has been made, exceeds 10% of the product of the
Fair Market Value per Common Share as of the Expiration Time times the number of
Common Shares outstanding (including any tendered shares) on the Expiration
Time, then, and in each such case, immediately prior to the opening of business
on the day after the date of the Expiration Time, the Per Share Price shall be
reduced (but not increased) so that the same shall equal the price determined by
multiplying the Per Share Price immediately prior to the close of business as of
the Expiration Time by a fraction (i) the numerator of which shall be equal to
(A) the product of (x) the Fair Market Value per Common Share as of the
Expiration Time and (y) the number of Common Shares outstanding (including any
tendered shares) as of the Expiration Time less (B) the amount of cash plus the
fair market value (determined as aforesaid) of the aggregate consideration
payable to stockholders based on the transactions described in clauses (I), (II)
and (III) above (based on, in the case of clause (I), the Common Shares accepted
for payment in such tender or exchange offer), and (ii) the denominator of which
shall be equal to the product of (A) the Fair Market Value per Common Share as
of the Expiration Time and (B) the number of Common Shares outstanding
(including any tendered shares) as of the Expiration Time less the number of
Common Shares accepted for payment in such tender or exchange offer.

     (g) NOTICES OF ADJUSTMENT.

          (i) Upon any adjustment of the Per Share Price pursuant to this
     Section 2.1, the Optionee shall promptly, but in any event within 10 days
     thereafter, cause to be given to each Noteholder, in accordance with
     Section 5.1, by registered mail, postage prepaid, a certificate signed by
     an executive officer setting forth the Per Share Price and/or the kind of
     shares of other securities or assets issuable upon the exercise by the
     Optionee of its option hereunder as so adjusted and describing in
     reasonable detail the facts accounting for such adjustment and the method
     of calculation used. Where appropriate, such certificate may be given in
     advance and included as a part of the notice required to be mailed under
     the other provisions of this Section 2.1.

          (ii) In the event the Optionee proposes to take (or receives notice
     of) any action which would require an adjustment of the Per Share Price
     pursuant to Section 2.1, then the Optionee shall cause to be given to each
     Noteholder, in accordance with Section 5.1, at least 10 days prior to the
     applicable record date or effective date for such action, a written notice
     in accordance with Section 2.1: (A) stating such record date or effective
     date, (B) describing such action in reasonable detail and (C) stating the
     date as of which it

                                       -7-





     is expected that holders of record of Common Shares shall be entitled to
     receive any applicable dividends or distributions or to exchange their
     shares for securities or other property, if any, deliverable upon such
     action. The failure to give the notice required by this Section 2.1(d) or
     any defect therein shall not affect the legality or validity of any such
     action or the vote upon any such action.

     (h) ADJUSTMENTS. No adjustments in the Per Share Price shall be made unless
such adjustment would result in an adjustment of more than 1% in the Per Share
Price; PROVIDED, HOWEVER, that any adjustments that by reason of this paragraph
(h) are not made shall be carried forward and taken into account in any
subsequent adjustment.

     (i) DEFINED TERMS. As used in this Section 2.1, the following terms shall
have the following meanings:

     "CONVERTIBLE SECURITIES" means any rights, warrants, options or other
securities directly or indirectly convertible into or exercisable or
exchangeable for Common Shares, other than any Permitted Issuances.

     "DETERMINATION DATE" means, with respect to the making of any issuance,
dividend or distribution as to which a record or other date is fixed for the
determination of holders of Common Shares entitled to receive or participate in
such issuance, dividend or distribution, the earlier of (i) such record or other
date and (ii) the first date on which the Common Shares trade regular way on the
principal securities exchange or market on which they are traded without the
right to receive such issuance, dividend or distribution.

     "FAIR MARKET VALUE" means, as of any date, with respect to a Common Share,
the average of the closing prices of a Common Share for the ten consecutive
trading days immediately prior to the determination date or, if the Common
Shares are not listed or admitted to trade on any national securities exchange,
the fair market value per share as determined in good faith by the Board of
Directors of the Optionee in reliance upon an opinion of a nationally recognized
investment bank and certified in a resolution sent to each Noteholder.

     "PERMITTED ISSUANCE" means (a) any shares, warrants, options, rights or
other securities of the Optionee outstanding on the date hereof (and the
issuance of any Common Shares upon the exercise or conversion thereof), (b) any
Common Shares issued upon exercise of the Warrants, (c) any share options or
other securities of the Optionee granted pursuant to any employee benefit plan
or program of the Optionee and any Common Shares or other securities of the
Optionee issued upon exercise thereof, (d) any securities of the Optionee issued
in consideration for the acquisition of a business and (e) any public offering
of any securities of the Optionee, other than pursuant to or in connection with
an issuance of rights, options or warrants to all holders of Common Shares of
the Optionee entitling them to subscribe for or purchase Common Shares.

     "WARRANTS" means the warrants to purchase 1,714,285 Common Shares sold
pursuant to the Warrant Agreement among the Optionee and Berkshire Hathaway
Inc., dated as of May 31, 2001.


                                       -8-





                                   ARTICLE III
                          CONDITIONS TO PURCHASE RIGHT

     SECTION 3.1 CONDITIONS TO PURCHASE RIGHT. The obligations of each
Noteholder to sell its Notes to the Optionee pursuant to this Agreement are
subject to the satisfaction or waiver by such Noteholder on or prior to the
Maturity Date of the following conditions:

     (a) NO EVENT OF DEFAULT. No Event of Default under such Noteholder's Notes
shall have occurred and be continuing.

     (b) HSR. If filing under the Hart-Scott-Rodino Antitrust Improvements Act
of 1976, as amended (the "HSR Act") is required in connection with sale of such
Noteholder's Notes to the Optionee hereunder, then any waiting period (and any
extension thereof) applicable to the transactions contemplated hereby under the
HSR Act shall have been terminated or shall have otherwise expired; PROVIDED,
that this condition shall only apply to a Noteholder if such Noteholder shall
have used its commercially reasonable efforts to pursue such termination or
expiration.

     (c) NYSE. The Common Shares (or other common equity securities to be issued
pursuant to Section 2.1(c)) to be issued at the Closing shall have been approved
for listing on the New York Stock Exchange, subject to official notice of
issuance.


                                   ARTICLE IV
                              ASSIGNMENT; NOVATION

     SECTION 4.1 ASSIGNMENT. Except for assignments (i) by the Optionee in
connection with any transaction described in Section 2.1(c) pursuant to which an
adjustment is made in the kind and amount of consideration payable to the
Noteholders upon exercise of the option granted hereby or (ii) by the Noteholder
that occur in accordance with Section 4.2, neither this Agreement nor any of the
rights, interests or obligations under this Agreement shall be assigned, in
whole or in part, by operation of law or otherwise by any of the parties without
the prior written consent of the other parties, and any such assignment that is
not consented to shall be null and void. Subject to the preceding sentence, this
Agreement will be binding upon, inure to the benefit of, and be enforceable by,
the parties and their respective successors and assigns.

     SECTION 4.2 NOVATION. In connection with any transfer by a Noteholder (a
"Transferring Noteholder") of all or any portion of any Note (other than a
purchase of a Note by the Optionee pursuant to Article I hereof), by operation
of law or otherwise, that is permitted under the Note, the transferee shall
execute and deliver to the Optionee a novation agreement in the form of Exhibit
1 hereto (a "Novation Agreement"). Execution and delivery to the Optionee of a
Novation Agreement shall, with effect from and after the consummation of the
transfer of the Note to the transferee, effect a novation of this Agreement and
shall have the following consequences, in addition to those provided by law: (A)
the Transferring Noteholder shall be discharged and released from all of its
obligations hereunder with respect to such portion of the Note transferred by it
to the transferee; and (B) the transferee shall become a Noteholder for all

                                       -9-





purposes hereunder with respect to the Note transferred to it. Each of the
Optionee and each Noteholder agrees, by its execution and delivery of this
Agreement or of a Novation Agreement, that any such novation of this Agreement
shall be binding upon the Optionee or such Noteholder without the need for
further action by the Optionee or such Noteholder. Upon a transferee's execution
and delivery to the Optionee of a Novation Agreement, the Optionee shall deliver
to such transferee a copy of any Exercise Notice theretofore delivered by the
Optionee. If an Exercise Notice has been delivered by the Optionee prior to any
transfer of a Note, the Transferring Noteholder shall, prior to the consummation
of such transfer, deliver a copy of the Exercise Notice to the transferee. Any
Exercise Notice delivered to the transferring Noteholder prior to a transfer of
a Note shall be binding upon the transferee.


                                    ARTICLE V
                               GENERAL PROVISIONS

     SECTION 5.1 NOTICES. All notices, requests, claims, demands and other
communications under this Agreement shall be in writing and shall be delivered
personally, by facsimile (which is confirmed as provided below) or by overnight
courier (providing proof of delivery) to the parties at the following addresses
(or at such other address for a party as shall be specified by like notice):

          (i) if to the Optionee, to

              White Mountains Insurance Group, Ltd.
              12 Church Street
              Suite 22A
              Hamilton HM11
              Bermuda
              Fax: 441-296-9904
              Attention: Tom Kemp

              with a copy to:

              White Mountains Insurance Group, Ltd.
              80 South Main Street
              Hanover, NH  03755
              Fax: 603-643-4562
              Attention: Tom Kemp

          (ii) if to the Noteholder, to the address shown opposite its name on
     Schedule 1 to this Agreement or on the relevant Novation Agreement, as
     applicable, or such other address as the Noteholder shall provide to the
     Optionee.

Notice given by personal delivery or overnight courier shall be effective upon
actual receipt. Notice given by facsimile shall be confirmed by appropriate
answer back and shall be effective upon actual receipt if received during the
recipient's normal business hours, or at the beginning of

                                      -10-





the recipient's next business day if not received during the recipient's normal
business hours. All notices by facsimile shall be confirmed promptly after
transmission in writing by personal delivery or overnight courier.

     SECTION 5.2 INTERPRETATION. When a reference is made in this Agreement to a
Section, Schedule or Exhibit, such reference shall be to a Section of, or a
Schedule or Exhibit to, this Agreement unless otherwise indicated. The headings
contained in this Agreement are for reference purposes only and shall not affect
in any way the meaning or interpretation of this Agreement. Whenever the words
"include", "includes" or "including" are used in this Agreement, they shall be
deemed to be followed by the words "without limitation". Whenever the singular
is used herein, the same shall include the plural, and whenever the plural is
used herein, the same shall include the singular, where appropriate.

     SECTION 5.3 ENTIRE AGREEMENT; THIRD-PARTY BENEFICIARIES. This Agreement
(including all exhibits and schedules hereto) constitutes the entire agreement,
and supersedes all prior agreements, understandings, representations and
warranties, both written and oral, among the parties with respect to the subject
matter of this Agreement. This Agreement is not intended to confer upon any
person other than the parties hereto any rights or remedies.

     SECTION 5.4 GOVERNING LAW. This Agreement shall be governed by, and
construed in accordance with, the laws of the State of New York, regardless of
the laws that might otherwise govern under applicable principles of conflicts of
laws thereof.

     SECTION 5.5 ENFORCEMENT. The parties agree that irreparable damage would
occur in the event that any of the provisions of this Agreement were not
performed in accordance with their specific terms or were otherwise breached. It
is accordingly agreed that the parties shall be entitled to an injunction or
injunctions to prevent breaches of this Agreement and to enforce specifically
the terms and provisions of this Agreement in any court of the United States or
any state court which in either case is located in the City of New York (any
such federal or state court, a "New York Court"), in addition to any other
remedy to which they are entitled at law or in equity. In addition, each of the
parties hereto (i) consents to submit itself exclusively to the personal
jurisdiction of any New York Court in the event any dispute arises out of this
Agreement or any of the transactions contemplated by this Agreement and (ii)
agrees that it will not attempt to deny or defeat such personal jurisdiction or
venue by motion or other request for leave from any such New York Court. Each
party further agrees that service of any process, summons, notice or document by
U.S. registered mail to such party's respective address set forth above shall be
effective service of process for any action, suit or proceeding in New York with
respect to any matters to which it has submitted to jurisdiction in this Section
5.5.

     SECTION 5.6 SEVERABILITY; AMENDMENT; WAIVER.

     (a) Whenever possible, each provision or portion of any provision of
this Agreement will be interpreted in such manner as to be effective and
valid under applicable law, but if any provision or portion of any provision
of this Agreement is held to be invalid, illegal or unenforceable in any
respect under any applicable law or rule in any jurisdiction, such
invalidity, illegality or unenforceability will not affect any other
provision or portion of any provision in such jurisdiction, and this
Agreement will be

                                      -11-





reformed, construed and enforced in such jurisdiction as if such invalid,
illegal or unenforceable provision or portion of any provision had never been
contained herein.

     (b) Except for novations pursuant to Section 4.2 hereof, this Agreement may
be amended only by a written instrument signed by each of the parties.

     (c) No delay on the part of any party in exercising any right, power or
privilege hereunder shall operate as a waiver thereof, nor shall any waiver on
the part of any party of any right, power or privilege, nor any single or
partial exercise of any such right, power or privilege, preclude any further
exercise thereof or the exercise of any other such right, power or privilege.

     SECTION 5.7 COUNTERPARTS. This Agreement may be executed in one or more
counterparts, all of which shall be considered one and the same agreement and
shall become effective when one or more counterparts have been signed by each of
the parties and delivered to the other parties.


                                      -12-





     IN WITNESS WHEREOF, the Noteholders and the Optionee have caused this
Agreement to be signed by their respective officers thereunto duly authorized,
all as of the date first written above.

                                       CGU INTERNATIONAL HOLDINGS
                                       LUXEMBOURG S.A.


                                       By
                                       Name:
                                       Title:


                                       CGU HOLDINGS LLC



                                       By
                                       Name:
                                       Title:


                                       WHITE MOUNTAINS INSURANCE
                                       GROUP, LTD.


                                       By
                                       Name:
                                       Title:



                                      -13-





                                                                      SCHEDULE 1


                    Addresses for Notices to the Noteholders

CGU INTERNATIONAL HOLDINGS LUXEMBOURG S.A.
  Galerie Kons
  4th Floor
  26 Place de la Gare
  L-1616 LUXEMBOURG
  Fax:
  Attention:  William Gilson


       With a copy to:
       CGNU plc
       St. Helens
       1 Undershaft
       20th Floor
       London, ENGLAND
       EC3P 3DQ
       Fax: 020 7662 7700
       Attention: Group Company Secretary


CGU HOLDINGS LLC
  St. Helens
  1 Undershaft
  20th Floor
  London, ENGLAND
  EC3P 3DQ
  Fax: 020 7662 7700
  Attention: Richard Whitaker


       With a copy to:
       CGNU plc
       St. Helens
       1 Undershaft
       20th Floor
       London, ENGLAND
       EC3P 3DQ
       Fax: 020 7662 7700
       Attention:  Group Company Secretary







                                                                       EXHIBIT 1

                               NOVATION AGREEMENT


                                                                          [date]

White Mountains Insurance Group, Ltd.
80 South Main Street
Hanover, NH  03755
Attention:  Michael Paquette

        Re: Novation of Note Purchase Option Agreement

Ladies and Gentlemen:

     The undersigned proposes to acquire from [name of Noteholder] (the
"Transferring Noteholder") one or more subordinated promissory notes due
________, 2002 ("Notes") of TACK Holding Corp. in an aggregate principal amount
of $___________. The undersigned has been advised that the Notes are subject to
a Note Purchase Option Agreement dated as of ______, 2001, among White Mountains
Insurance Group, Ltd. (the "Optionee"), the Transferring Noteholder and the
other holders of Notes (the "Note Purchase Option Agreement"), pursuant to which
the Optionee has an option to purchase Notes from the holders thereof on the
terms and subject to the conditions set forth in such Agreement. By this letter,
the undersigned agrees that, with effect from and after the consummation of the
acquisition of the Notes to be acquired by the undersigned from the Transferring
Noteholder, the undersigned shall become a party to the Note Purchase Option
Agreement as a Noteholder (as defined in the Note Purchase Option Agreement) for
all purposes under the Note Purchase Option Agreement with respect to the Notes
acquired by it.

                                       Very truly yours,

                                       [Name of transferee]



                                       By:____________________________________
                                          Name:
                                          Title:
                                          Address for Notices:






                                                                       EXHIBIT 2

                      FORM OF REGISTRATION RIGHTS AGREEMENT