Exhibit 99.6

              TENTH AMENDMENT AND CONSENT TO THE HOLDINGS GUARANTY

            TENTH AMENDMENT AND CONSENT TO THE HOLDINGS GUARANTY (the "Tenth
Amendment"), dated as of April 8, 2003, among TRENWICK GROUP LTD., a company
organized under the laws of Bermuda ("Holdings") and the Banks party to the
Credit Agreement referred to below. Unless otherwise defined herein, capitalized
terms used herein and defined in the Holdings Guaranty referred to below are
used herein as so defined.

                              W I T N E S S E T H :

            WHEREAS, Trenwick America Corporation, a Delaware corporation (the
"Borrower"), Trenwick Holdings Ltd., a company organized under the laws of the
United Kingdom (the "Trenwick Holdings"), the lending institutions from time to
time party thereto (each a "Bank" and, collectively, the "Banks"), Wachovia
Bank, National Association (f/k/a First Union National Bank), as Syndication
Agent (the "Syndication Agent"), Fleet National Bank, as Documentation Agent
(the "Documentation Agent"), and JPMorgan Chase Bank (f/k/a The Chase Manhattan
Bank), as Administrative Agent (the "Administrative Agent"), are party to a
Credit Agreement, dated as of November 24, 1999 and amended and restated as of
September 27, 2000 (as the same has been amended, modified or supplemented to,
but not including, the date hereof, the "Credit Agreement");

            WHEREAS, Holdings and the Administrative Agent entered into a
Holdings Guaranty, dated as of September 27, 2000 (as the same has been amended,
modified or supplemented to, but not including, the date hereof, the "Holdings
Guaranty") in order to induce the Banks to make Loans to the Borrower and issue
Letters of Credit for the account of the Account Party and Guaranteed Creditors
(and Lending Affiliates thereof) to enter into Interest Rate Protection
Agreements and Other Hedging Agreements with the Borrower and/or the Account
Party; and

            WHEREAS, subject to the terms and conditions set forth below, the
parties hereto wish to amend the Holdings Guaranty as provided herein;

            NOW, THEREFORE, it is agreed;

A.    Consent

            1. Notwithstanding anything to the contrary contained in the Credit
Agreement or the Holdings Guaranty, the Banks hereby consent to (i) the
amendments and modifications to the Trenwick Senior Notes on the terms and
conditions set forth in the draft Second Supplemental Indenture to the Trenwick
Senior Notes (the "Draft Indenture"), dated as of April 1, 2003 and



attached hereto as Annex A, and (ii) the payment by the Borrower of $2,512,500
of accrued and unpaid interest required to be paid pursuant to the Trenwick
Senior Notes on April 1, 2003; provided, however, the parties hereto hereby
agree that the interest payment consented to in this clause (ii) may not be made
until the Second Supplemental Indenture (as defined below) has been delivered to
the Administrative Agent and is in full force and effect.

B.    Amendments

            1. Section 3.01 of the Holdings Guaranty is hereby amended by
inserting the following new subclause (t) immediately following subclause (s)
thereof:

            "(t) Run Off Reports. As soon as available, a copy of any written
      reports or other material information prepared by any representative of
      the holders of the Trenwick Senior Notes retained by Holdings and
      delivered either to a regulatory authority (unless such disclosure is
      prohibited by such regulatory authority) or the Senior Note Holders.

            2. Section 3.13(b) of the Holdings Guaranty is hereby amended by
redesignating clause (ii) appearing therein as clause (iii) and inserting the
following new clause (ii) immediately after the end of clause (i) thereof:

      "(ii) any Credit Party that the Administrative Agent determines in its
      reasonable discretion would not be in the Renewing Banks' interest to have
      authorize, execute and deliver the U.S. Pledge Agreement"

            3. Section 3.13(b) of the Holdings Guaranty is hereby further
amended by inserting the text "or similar agreement or agreements" immediately
after the text "Each pledge agreement" appearing therein.

            4. Section 3.14 of the Holdings Guaranty is hereby amended by
redesignating clause (iv) appearing therein as clause (v) and inserting the
following new clause (iv) immediately after the end of clause (iii) thereof:

      ", (iv) any Subsidiary of Holdings that the Administrative Agent
      determines in its reasonable discretion would not be in the Renewing
      Banks' interest to have authorize, execute and deliver a Guaranty"

            5. Section 3.15 of the Holdings Guaranty is hereby amended by (x)
inserting the reference "(i)" immediately preceding the text "where Legal
Requirements" and (y) inserting the following text at the end of the first
parenthetical appearing in said Section:

      "and (ii) that the Administrative Agent determines in its reasonable
      discretion would not be in the Renewing Banks' interest to have authorize,
      execute and deliver the U.S. Security Agreement"

            6. Section 3.16 of the Holdings Guaranty is hereby amended by (x)
inserting the reference "(i)" immediately preceding the text "where Legal
Requirements" and (y) inserting the following text at the end of the first
parenthetical appearing in said Section:


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      "and (ii) that the Administrative Agent determines in its reasonable
      discretion would not be in the Renewing Banks' interest to have authorize,
      execute and deliver a Foreign Security Agreement"

            7. Section 3.17(c) of the Holdings Guaranty is hereby amended by (i)
deleting the first parenthetical in its entirety appearing therein and inserting
the parenthetical "(and/or such additional or alternative guarantees as may be
determined necessary or desirable by the Administrative Agent in accordance with
the criteria described in Section 3.14 hereof, each such additional or
alternative guaranty, an "Additional Guaranty", and collectively, the
"Additional Guaranties")" in lieu thereof and (ii) deleting the text "modified
Subsidiaries Guaranty" appearing in the further proviso thereof and inserting
the text "Additional Guaranty" in lieu thereof.

            8. Section 3.18 of the Holdings Guaranty is hereby amended by
deleting the text "April 4, 2003" appearing therein and inserting the text
"April 25, 2003" in lieu thereof.

            9. Section 3.22 of the Holdings Guaranty is hereby amended by
deleting the text "March 1, 2003" appearing therein and inserting the text "July
15, 2003" in lieu thereof.

            10. Section 4.02(a) of the Holdings Guaranty is hereby amended by
inserting the text, "(s) ReCor Insurance Company Inc. may merge with INSCORP if
INSCORP is the surviving corporation of such merger" immediately preceding
clause (t) appearing in the proviso thereof.

            11. Schedule I to the Holdings Guaranty is hereby amended by
deleting the date "April 1, 2003" appearing in the definition of "Consolidated
Tangible Net Worth" and inserting the date "August 1, 2003" in lieu thereof.

            12. The definition of "Credit Documents" appearing in Schedule I to
the Holdings Guaranty is hereby amended by inserting the text "and each
Additional Guaranty" at the end thereof.

            13. The definition of "Credit Party" appearing in Schedule I to the
Holdings Guaranty is hereby amended to read in its entirety as follows:

            "Credit Party" shall mean each U.S. Credit Party and each Foreign
      Credit Party.

            14. The definition of "Foreign Credit Party" appearing in Schedule I
to the Holdings Guaranty is hereby amended to read in its entirety as follows:

            "Foreign Credit Party" shall mean Holdings, the Account Party and
      each Foreign Subsidiary of Holdings which is party to a Subsidiary
      Guaranty.

            15. The definition of "Subsidiary Guaranty" appearing in Schedule I
to the Holdings Guaranty is hereby amended by (i) deleting the word "and"
immediately following the text "U.S. Subsidiary Guaranty" and inserting a comma
in lieu thereof and (ii) and inserting the text "and each Additional Guaranty"
immediately preceding the period at the end of said definition.


                                      -3-


            16. The definition of "U.S. Credit Party" appearing in Schedule I to
the Holdings Guaranty is hereby amended to read in its entirety as follows:

            "U.S. Credit Party" shall mean the Borrower and each Subsidiary of
      Holdings which is organized under the laws of the United States or any
      State or territory thereof and is party to a Subsidiary Guaranty.

            17. Section I of the Holdings Guaranty is hereby further amended by
inserting the following new defined term in the appropriate alphabetical order:

            "Additional Guaranties" shall have the meaning provided in Section
      3.17(c) of the Holdings Guaranty.

C.    Miscellaneous Provisions

            1. In order to induce the Banks to enter into this Tenth Amendment,
Holdings hereby represents and warrants that (i) the representations and
warranties of Holdings contained in the Holdings Guaranty are true and correct
in all material respects on and as of the Tenth Amendment Effective Date (as
defined below) (except with respect to any representations and warranties
limited by their terms to a specific date, which shall be true and correct in
all material respects as of such date), and (ii) there exists no Default or
Event of Default under the Credit Agreement on the Tenth Amendment Effective
Date (as defined below) after giving effect to this Tenth Amendment.

            2. This Tenth Amendment is limited as specified and shall not
constitute an amendment, modification, acceptance or waiver of any other
provision of the Holdings Guaranty or any other Credit Document.

            3. THIS TENTH AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE
PARTIES HEREUNDER SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAW
OF THE STATE OF NEW YORK.

            4. This Tenth Amendment shall become effective on the date (the
"Tenth Amendment Effective Date") when (i) Holdings and the Required Banks shall
have signed a counterpart hereof (whether the same or different counterparts)
and shall have delivered (including by way of telecopier) the same to the
Administrative Agent, (ii) the Borrower, each Account Party and the Required
Banks shall have consented to the Ninth Amendment and Waiver to the Credit
Agreement, dated as of April 8, 2003; provided that to the extent that the
Second Supplemental Indenture, dated April 1, 2003, among the Borrower and the
parties thereto, which shall be on the same terms and conditions as the Draft
Indenture (the "Second Supplemental Indenture"), is not in full force and effect
within one business day after the effectiveness of this Tenth Amendment, this
Tenth Amendment shall be rescinded and shall be null and void with none of the
consents, waivers or amendments contained herein to have any effect whatsoever
and with the Banks having the same rights and remedies in connection with the
Credit Documents as if this Tenth Amendment was never effective.


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            5. From and after the Tenth Amendment Effective Date, all references
in the Holdings Guaranty and in the other Credit Documents shall be deemed to be
referenced to the Holdings Guaranty as modified hereby.

                                      * * *


                                      -5-


            IN WITNESS WHEREOF, the undersigned have caused this Tenth Amendment
to be duly executed and delivered as of the date first above written.

                                                 TRENWICK GROUP LTD.


                                                 By: /s/ Alan L. Hunte
                                                    ---------------------------
                                                 Name: Alan L. Hunte
                                                 Title: Chief Financial Officer



                                               [NAME OF LENDER]


                                               By:
                                                  ---------------------------
                                                  Name:
                                                  Title:

        [Signature Page to the Tenth Amendment to the Holdings Guaranty]