THIRD SUPPLEMENTAL INDENTURE (the "Supplemental  Indenture"),  dated as
of  September  27,  2000,  among  Trenwick  Group Inc.,  a Delaware  corporation
("Trenwick"),  Trenwick America Corporation,  a Delaware corporation  ("Trenwick
America")  and  State  Street  Bank and  Trust  Company,  as  trustee  under the
Indenture referred to below (the "Trustee").

                               W I T N E S S E T H


         WHEREAS, pursuant to the Indenture (the "Original Indenture"), dated as
of December 1, 1995, between Piedmont  Management Company Inc.  ("Piedmont") and
the Trustee,  Piedmont  issued its  Contingent  Interest Notes Due June 30, 2006
(collectively, the "Securities");

         WHEREAS,  on December 13, 1995, Piedmont merged with and into Chartwell
Re  Corporation  ("Chartwell"),  and  upon  consummation  of  such  merger  (the
"Piedmont  Merger"),  all of the debts,  liabilities,  duties and obligations of
Piedmont  became the debts,  liabilities,  duties and  obligations of Chartwell,
including, without limitation, the debts, liabilities, duties and obligations of
Piedmont under the Original Indenture;

         WHEREAS,  on consummation of the Piedmont Merger, the assumption of the
debts,  liabilities,  duties and  obligations  of  Piedmont  under the  Original
Indenture was evidenced by the execution and delivery by Piedmont, Chartwell and
the Trustee of a First Supplemental Indenture dated as of December 13, 1995 (the
"First Supplement");

         WHEREAS,  on October 27, 1999,  Chartwell merged with and into Trenwick
(the "Chartwell Merger"),  and upon consummation of the Chartwell Merger, all of
the debts,  liabilities,  duties and obligations of Chartwell  became the debts,
liabilities,  duties and obligations of Trenwick, including, without limitation,
the debts,  liabilities,  duties and obligations of Chartwell under the Original
Indenture, as amended by the First Supplement;

         WHEREAS, on consummation of the Chartwell Merger, the assumption of the
debts,  liabilities,  duties and  obligations  of  Chartwell  under the Original
Indenture,  as amended by the First  Supplement,  was evidenced by the execution
and delivery by  Chartwell,  Trenwick  and the Trustee of a Second  Supplemental
Indenture dated as of October 27, 1999 (the "Second Supplement" and the Original
Indenture, as so supplemented by the First Supplement and the Second Supplement,
the "Indenture");

         WHEREAS,  Trenwick, LaSalle Re Holdings Limited, LaSalle Re Limited and
Trenwick Group Ltd. (formerly Gowin Holdings International Limited) have entered
into an Amended  and  Restated  Agreement,  Schemes of  Arrangement  and Plan of
Reorganization,  dated as of March 20, 2000, in connection  with which  Trenwick
will transfer  substantially  all of its assets and  liabilities to Chartwell Re
Holdings Corporation  ("Chartwell Re") and Chartwell Re will merge with and into
Trenwick America (the "Asset Transfer");


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         WHEREAS,  upon  consummation of the Asset  Transfer,  all of the debts,
liabilities,   duties  and  obligations  of  Trenwick  will  become  the  debts,
liabilities,  duties and  obligations  of Trenwick  America,  including  without
limitation the debts, liabilities,  duties and obligations of Trenwick under the
Indenture;

         WHEREAS,  Section 5.1 of the Indenture  provides in pertinent part that
Trenwick may  consummate  the Asset  Transfer,  and that, in the event  thereof,
Trenwick America shall expressly assume, by supplemental indenture, executed and
delivered  to  the  Trustee,  all of  the  obligations  of  Trenwick  under  the
Indenture;

         WHEREAS,  Section 5.1 of the Indenture  provides in pertinent part that
in connection  with the Asset  Transfer,  Trenwick is required to deliver to the
Trustee an Officers'  Certificate  and an Opinion of Counsel,  each stating that
the Asset Transfer and supplemental indenture in respect thereto comply with the
provisions described in the Indenture and that all conditions precedent provided
for in the Indenture relating to such transaction have been complied with;

         WHEREAS,  Section 5.2 of the Indenture  provides in pertinent part that
upon the Asset  Transfer,  the successor  Person to which  Trenwick  transferred
substantially  all of its  assets  and  liabilities  shall  succeed  to,  and be
substituted  for, and may exercise  every right and power of Trenwick  under the
Indenture  with the same  effect as if such  successor  Person had been named as
Trenwick therein;

         WHEREAS,  Section 9.1 of the Indenture  provides in pertinent part that
Trenwick and the Trustee may supplement the Indenture without the consent of any
Holder of a Security to provide for the  assumption  of  Trenwick's  obligations
under the  Indenture  to the  Holders in the case of a transfer  by  Trenwick of
substantially  all of its assets  pursuant  to Article 5 of the  Indenture  upon
request of Trenwick  accompanied  by a  resolution  of the Board of Directors of
Trenwick authorizing the execution of such supplemental indenture; and

         WHEREAS,  all things necessary to make this Supplemental  Indenture and
the statements in the Officers'  Certificate and opinion of Counsel delivered in
connection  therewith a valid and binding  agreement  of Trenwick  and  Trenwick
America in accordance with its terms have been done;

         NOW,  THEREFORE,  for  and  in  consideration  of the  premises,  it is
mutually  covenanted and agreed for the equal and  proportionate  benefit of all
Holders of the Securities as follows:

         SECTION  1.  Trenwick  America  hereby  expressly  assumes  all  of the
obligations of Trenwick  under the  Indenture,  including the obligation to make
due and  punctual  payment of the Payment  Amount and the  performance  of every
covenant, agreement and obligation on the part of Trenwick under the Indenture.

                                       2



         SECTION 2. Pursuant to Section 5.2 of the Indenture,  Trenwick  America
hereby  succeeds to, and is  substituted  for, and may exercise  every right and
power of  Trenwick  under the  Indenture  with the same  effect  as if  Trenwick
America had been named as Trenwick therein.

         SECTION  3.  After the  execution  and  delivery  of this  Supplemental
Indenture, any Securities authenticated and delivered in substitution for, or in
lieu of,  Securities then outstanding and all Securities  presented or delivered
to the Trustee on and after such date for such purpose  shall be stamped,  typed
or otherwise affixed with a notation as follows:

                  TRENWICK  AMERICA  CORPORATION,  A DELAWARE  CORPORATION,  HAS
                  EXPRESSLY   ASSUMED  ALL  OF  THE   OBLIGATIONS   OF  PIEDMONT
                  MANAGEMENT COMPANY INC., CHARTWELL RE CORPORATION AND TRENWICK
                  GROUP INC.  UNDER THE  INDENTURE,  INCLUDING THE OBLIGATION TO
                  MAKE  DUE AND  PUNCTUAL  PAYMENT  OF THE  PAYMENT  AMOUNT  (AS
                  DEFINED  IN  THE  INDENTURE)  AND  THE  PERFORMANCE  OF  EVERY
                  COVENANT,  AGREEMENT AND OBLIGATION ON THE PART OF THE COMPANY
                  UNDER THE  INDENTURE.  REFERENCE  IS HEREBY  MADE TO THE THIRD
                  SUPPLEMENTAL INDENTURE, DATED AS OF SEPTEMBER 27, 2000, COPIES
                  OF WHICH ARE ON FILE WITH THE TRUSTEE.

         SECTION 4. The Trustee accepts this  Supplemental  Indenture and agrees
to execute the trust  created by the Indenture as hereby  supplemented  upon the
terms  and  conditions  set  forth in the  Indenture,  including  the  terms and
provisions  defining and limiting the  liabilities and  responsibilities  in the
performance of the trust created by the Indenture as hereby supplemented.

         SECTION 5. The Indenture,  supplemented as hereinabove set forth, is in
all  respects  ratified and  confirmed,  and the terms and  conditions  thereof,
supplemented  as  hereinabove  set forth,  shall be and remain in full force and
effect.

         SECTION 6. The recitals  contained in this  Supplemental  Indenture and
the statements in the Officers'  Certificate and Opinion of Counsel delivered in
connection  herewith  shall be taken  as  statements  of  Trenwick  America  and
Trenwick, and the Trustee shall have no responsibility for their correctness.

         SECTION 7. This Supplemental Indenture shall become effective upon, and
simultaneously with, the effective time of the Asset Transfer.



                                       3



         SECTION 8. The internal laws of the State of New York shall govern this
Supplemental Indenture.

         SECTION 9. This  Supplemental  Indenture may be signed in any number of
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

         SECTION 10. Capitalized  terms not otherwise defined herein are defined
as set forth in the Indenture.

         IN WITNESS  WHEREOF,  the parties hereto have caused this  Supplemental
Indenture to be duly executed as of the date first above written.

                                    TRENWICK AMERICA CORPORATION


                                    By: /s/ James F. Billett, Jr.
                                        ----------------------------------
                                        Name:  James F. Billett, Jr.
                                        Title: Chairman, President and Chief
                                               Executive Officer
Attest:


By:  /s/ John V. Del Col
     -----------------------
     Name:    John V. Del Col
     Title:   Senior Vice President
              General Counsel and
              Secretary

                                    TRENWICK GROUP INC.


                                    By: /s/ James F. Billett, Jr.
                                        ----------------------------------
                                        Name:  James F. Billett, Jr.
                                        Title: Chairman, President and Chief
                                               Executive Officer
Attest:


By:  /s/ John V. Del Col
     -----------------------
     Name:  John V. Del Col
     Title: Senior Vice President,
            General Counsel and
            Secretary

                                    STATE STREET BANK AND TRUST COMPANY


                                    By: /s/ Kathy A. Larimore
                                        ----------------------------------
                                        Name:   Kathy A. Larimore
                                        Title:  Assistant Vice President
Attest:

By:  /s/ Susan T. Keller
     -----------------------
     Name:   Susan T. Keller
     Title:  Vice President



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