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                                                                    EXHIBIT 4.25

                                                                  CONFORMED COPY

                           NOVATION AND AMENDMENT DEED

                             DATED 26TH MARCH, 2003

                                     BETWEEN

                                   MARCONI PLC

                             MARCONI CORPORATION PLC

                         MARCONI (BRUTON STREET) LIMITED

                                       AND

                               FINMECCANICA S.P.A.

              IN RESPECT OF AN AGREEMENT FOR THE SALE AND PURCHASE
                    OF THE ENTIRE ISSUED SHARE CAPITAL OF MMH
                           DATED AS OF 2ND AUGUST 2002

                                 ALLEN & OVERY

                                     London

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                                    CONTENTS
<TABLE>
<CAPTION>
CLAUSE                                                                       PAGE
<S>      <C>                                                                 <C>
1.       Definitions and Interpretation....................................   1
2.       Representations and Warranties....................................   2
3.       Novation..........................................................   2
4.       Agreement Amendment...............................................   3
5.       Notices...........................................................   4
6.       Counterparts......................................................   4
7.       Third Parties.....................................................   4
8.       Governing law.....................................................   4
</TABLE>

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THIS DEED is made on 26th March, 2003

BETWEEN:

(1)      MARCONI PLC, having its registered office at New Century Park, PO Box
         53, Coventry CV3 1HJ, England (EXISTING GUARANTOR);

(2)      MARCONI CORPORATION PLC, having its registered office at New Century
         Park, PO Box 53, Coventry CV3 1HJ, England (NEW GUARANTOR);

(3)      MARCONI (BRUTON STREET) LIMITED, having its registered office at New
         Century Park, PO Box 53, Coventry CV3 1HJ, England (MARCONI); and

(4)      FINMECCANICA S.P.A., having its registered office at Piazza Monte
         Grappa 4, Rome, Italy (the PURCHASER).

WHEREAS

(A)      By an agreement dated 2nd August 2002 between the Existing Guarantor,
         Marconi and the Purchaser (the AGREEMENT), Marconi agreed to sell and
         transfer, and the Purchaser agreed to purchase, the MMH Shares. In
         accordance with clause 12 of the Agreement, the Existing Guarantor
         unconditionally and irrevocably (i) guaranteed to the Purchaser the
         full, due and punctual payment and observation by Marconi of all its
         obligations under the Agreement and the Share Purchase Documents to
         which Marconi was a party and (ii) indemnified the Purchaser
         immediately on demand against any cost, loss or liability suffered by
         it if any obligation guaranteed by it is or becomes unenforceable,
         invalid or illegal.

(B)      The Marconi Corporate Restructuring (as defined in sub-clause 12.7 of
         the Agreement) will be effected, as from the Effective Time, pursuant
         to the New Guarantor Scheme (as such terms are defined below).

(C)      In accordance with sub-clause 12.7 of the Agreement, the parties have
         agreed that with effect from the Effective Time, the Existing Guarantor
         (upon ceasing to be the ultimate parent company of the Marconi Group)
         shall be released from, and the New Guarantor shall assume, the
         Existing Guarantor's rights, obligations, duties and liabilities under
         the Agreement, on the terms and subject to the conditions hereinafter
         provided.

(D)      The Existing Guarantor, the New Guarantor, Marconi and the Purchaser
         have agreed to enter into this Deed novating and amending the
         Agreement.

In consideration of the provisions and mutual covenants contained in this Deed
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged by each of the parties hereto,

IT IS AGREED AS FOLLOWS:

1.       DEFINITIONS AND INTERPRETATION

1.1      Definitions

         In this Deed the following expressions shall have the following
meanings:

                                       1

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         EFFECTIVE TIME means for the purposes of this Deed in relation to the
         New Guarantor Scheme the date upon which an office copy of the order of
         the High Court of England and Wales sanctioning that New Guarantor
         Scheme shall have been delivered to the Registrar of Companies for
         registration.

         NEW GUARANTOR SCHEME means the proposed scheme of arrangement in
         respect of the New Guarantor pursuant to section 425 of the Companies
         Act 1985 (as amended) to be sanctioned on or around May 2003.

         NOVATED AGREEMENT shall mean the AGREEMENT as novated, amended and
         supplemented by this Deed.

         REGISTRAR OF COMPANIES means the registrar or other officer performing
         under the Companies Act 1985 (as amended) the duty of registration of
         companies in England and Wales including a deputy registrar.

1.2      In this Deed, unless the contrary appears, a reference to:

         (a)      PARTY is a party to this Deed;

         (b)      a person includes its successors and assigns;

         (c)      a provision of law is a reference to that provision as amended
                  or re-enacted; and

         (d)      a time of day is a reference to London time.

1.3      Unless the contrary intention appears a term defined in the Agreement
         has the same meaning where used in this Deed.

1.4      The clause and sub-clause headings in this Deed are for convenience
         only and are to be ignored in construing this Deed.

2.       REPRESENTATIONS AND WARRANTIES

2.1      The New Guarantor represents and warrants to the Purchaser on the terms
         set out in the Schedule to this Deed as at the Effective Time, by
         reference to the circumstances then existing.

2.2      The Existing Guarantor warrants, for the benefit of the New Guarantor,
         that save in relation to claims already notified to it by the
         Purchaser, it is not aware of any claim (actual or threatened) by the
         Purchaser against the Existing Guarantor under the Agreement.

2.3      In consideration for the representations and warranties given by the
         New Guarantor in sub-clause 2.1 above, with effect from the Effective
         Time, the parties agree that the New Guarantor shall have no liability
         in respect of the Warranties given under paragraph 1 of schedule 4 of
         the Agreement in respect of the Existing Guarantor.

2.4      The representations and warranties set out in sub-clause 2.1 above
         shall survive the execution and delivery of this Deed.

3.       NOVATION

3.1      With effect from the Effective Time:

                                       2

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         (a)      the Existing Guarantor is released and discharged from its
                  obligations, duties and liabilities under the Agreement;

         (b)      the Existing Guarantor agrees that it has no rights under the
                  Agreement;

         (c)      the New Guarantor agrees to (i) assume the rights,
                  obligations, duties and liabilities of the Existing Guarantor
                  under the Agreement and (ii) perform all the obligations of
                  the Existing Guarantor under the Agreement in favour of the
                  Purchaser as if the New Guarantor had been a party to the
                  Agreement in place of the Existing Guarantor;

         (d)      the parties consent to and accept the assumption by the New
                  Guarantor of the Existing Guarantor's rights, obligations,
                  duties and liabilities under the Agreement and the release and
                  discharge of the Existing Guarantor from its obligations,
                  duties and liabilities under the Agreement;

         (e)      each of the other parties to the Novated Agreement agrees with
                  the New Guarantor to perform its obligations under the
                  Agreement (as amended and supplemented by this Deed) in favour
                  of the New Guarantor,

         each of the foregoing events and agreements being conditional on, and
         taking effect simultaneously with, the others.

3.2      With effect from the Effective Time, the New Guarantor hereby agrees
         that all of the Purchaser's rights, claims, actions, demands and
         proceedings whatsoever and howsoever arising out of or in respect of
         the Share Purchase Documents, (including any such accrued rights which
         have arisen against the Existing Guarantor prior to the Effective Time,
         and any such rights arising against the New Guarantor after the
         Effective Time) shall be enforceable by the Purchaser against the New
         Guarantor.

3.3      Notwithstanding clause 3.1 above, the Existing Guarantor and the New
         Guarantor are each released from any obligations under the Novated
         Agreement to the extent that such obligations have been fully
         performed, satisfied or otherwise fully complied with in accordance
         with the Agreement by the Existing Guarantor as at the Effective Time.

4.       AGREEMENT AMENDMENT

4.1      With effect from the Effective Time the Agreement will be amended as
         follows:

         (a)      the expression "MARCONI PLC" wherever it appears in the
                  Agreement will be deleted and replaced with "MARCONI
                  CORPORATION PLC";

         (b)      where the context so permits, the expression "THIS AGREEMENT"
                  wherever it appears in the Agreement shall be treated as
                  though it referred to the Novated Agreement;

         (c)      for the purposes of sub-clause 18.4 of the Agreement, the
                  address details for the New Guarantor shall be as follows:

<TABLE>
<CAPTION>
Name of party        Addressee         Address            Facsimile No.      E-mail address
<S>                  <C>               <C>                <C>                <C>
Marconi              The Company       4th Floor,         +44 20 7306 1395   Mary.Skelly@
Corporation plc      Secretary         Regents Place,
                                       338 Euston Rd,                        marconi.com
                                       London NW1 3BT,
                                       England
</TABLE>

                                       3

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4.2      The parties agree that, with effect from the Effective Time the
         Agreement is novated and constitutes an agreement between New Guarantor
         (as guarantor), Marconi and the Purchaser on the terms and conditions
         of the Novated Agreement. In particular, the New Guarantor shall
         perform all the guarantee and indemnification obligations in favour of
         the Purchaser under sub-clauses 12.1 to 12.6 of the Novated Agreement.

4.3      Save as amended hereby, the Agreement as novated remains in full force
         and effect.

5.       NOTICES

         All notices under or in connection with this Deed will, unless
         otherwise stated, be given in accordance with the Novated Agreement.

6.       COUNTERPARTS

         This Deed may be executed in any number of counterparts, and by the
         parties on separate counterparts. Each counterpart shall constitute an
         original of this Deed, and the counterparts together shall constitute
         one and the same document.

7.       THIRD PARTIES

         A person who is not a party to this Deed has no rights under the
         Contracts (Rights of Third Parties) Act 1999 to enforce any term of
         this Deed, but this does not affect any right or remedy of a third
         party which exists or is available apart from that Act.

8.       GOVERNING LAW

         This Deed shall be governed by and construed in accordance with English
         law. Any disputes that may arise out of or in connection with this Deed
         will settled by arbitration as provided in clause 28 of the Novated
         Agreement.

IN WITNESS of which this deed has been executed and has been delivered on the
date stated at the beginning of this Deed.

EXISTING GUARANTOR
EXECUTED as a deed by                      )     C. HOLDEN
Marconi plc                                )     Director
acting by C. HOLDEN                        )     M. SKELLY
and M. SKELLY                              )     Director/Secretary

NEW GUARANTOR
EXECUTED as a deed by                      )     C. HOLDEN
Marconi Corporation plc                    )     Director
acting by C. HOLDEN                        )     M. SKELLY
and M. SKELLY                              )     Director/Secretary

                                       4

<PAGE>

MARCONI
EXECUTED as a deed by                      )     C. DONALDSON
Marconi (Bruton Street) Limited            )     Director
Acting by C.                               )     M. SKELLY
DONALDSON                                  )     Director/Secretary
and M. SKELLY

PURCHASER
EXECUTED as a deed by                      )     M. ORLANDO
Finmeccanica S.p.A                         )     Director
acting by M. ORLANDO                       )     V. SICA
and V. SICA                                )     Director/Secretary

                                       5

<PAGE>

                                   SCHEDULE 1

                                   WARRANTIES

         (a)      The New Guarantor is duly incorporated and validly existing
                  under the laws of England, and has the requisite power and
                  authority to enter into and perform its obligations under this
                  Deed and the Novated Agreement.

         (b)      This Deed and the Novated Agreement constitute binding
                  obligations of the New Guarantor.

         (c)      The execution and delivery of this Deed, and the performance
                  by the New Guarantor of its obligations under this Deed and
                  the Novated Agreement will (or with the giving of notice or
                  lapse of time or both would) not:

                  (i)      result in a breach of any provision of the memorandum
                           or articles of association of the New Guarantor; or

                  (ii)     result in a breach of any order, judgment or decree
                           of any court or governmental agency to which the New
                           Guarantor is a party or by which the New Guarantor is
                           bound or of any other contractual commitment to which
                           the New Guarantor is a party.

         (d)      The New Guarantor has full knowledge of the Agreement and is
                  fully aware of its terms and conditions, in particular of the
                  provisions contained in sub-clauses 12.1 to 12.6 thereof which
                  constitute the Marconi Guarantee .

         (e)      The New Guarantor shall be immediately after the Effective
                  Time, the ultimate parent company of the Marconi Group and the
                  company owning (directly or indirectly as a result of its
                  direct or indirect shareholdings in the members of the Marconi
                  Group) all or substantially all of the assets of the Marconi
                  Group.

         (f)      Each of Marconi and the Existing Guarantor have not assigned
                  or transferred any of their respective benefits or obligations
                  under any of the Share Purchase Documents to which they are a
                  party.

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