<PAGE>

                                                                    EXHIBIT 4.51

[CLIFFORD CHANCE PUNDER LOGO]

                                                                  CONFORMED COPY

                      MARCONI COMMUNICATIONS HOLDINGS GMBH

                                   AS PLEDGOR

                                       AND

                   THE LAW DEBENTURE TRUST CORPORATION p.l.c.

                         AS PLEDGEE AND SECURITY TRUSTEE

                                       AND

                                     OTHERS

   ---------------------------------------------------------------------------
                             SHARE PLEDGE AGREEMENT
             relating to the shares in Marconi Communications ONDATA
                                      GmbH

   ---------------------------------------------------------------------------

                                     - 1 -

<PAGE>

                                  NOTARIAL DEED

                                                        ROLL OF DEED NO. 48/2003

Recorded

at Basel this 15th day of May 2003

Before me, the undersigned

                                Dr. Thomas Gelzer

                                  notary public

with official offices in Basel (Switzerland) appeared today the following
persons:

1.       Ms. Muriel Krebs, born on March 31, 1978 having her business address at
         Aeschenvorstadt 4, 4010 Basel (Switzerland) personally known to the
         notary.

2.       Ms. Stefanie Brennwald, born on February 8, 1978, having her business
         address at Aeschenvorstadt 4, 4010 Basel (Switzerland) personally known
         to the notary.

The person appearing to 1. declared to make the following declarations not in
her own name but, excluding any personal liability, for and on behalf of

         MARCONI COMMUNICATIONS HOLDINGS GmbH, a limited liability company
         organised under the laws of the Federal republic of Germany, having its
         business address at Gerberstra(beta)e 33, D-71522 Backnang, which is
         registered in the commercial register (Handelsregister) of the local
         court (Amtsgericht) of Backnang under HRB 1563 (the "PLEDGOR"),

         Presenting a fax copy of the power of attorney dated May 13, 2003,
         promising to furnish the original as soon as possible.

The person appearing to 2. declared to make the following declarations not in
her own name but, excluding any personal liability, for and on behalf of

         THE LAW DEBENTURE TRUST CORPORATION p.l.c., having its business address
         at Fifth Floor, 100 Wood Street, London, EC2V 7EX, England in its
         capacity as security trustee under the Relevant Documents (as defined
         below) (the "SECURITY TRUSTEE" or the "PLEDGEE"),

         presenting a fax copy of the power of attorney dated May 14, 2003,
         promising to furnish the original as soon as possible.

                                     - 2 -

<PAGE>

Neither the Notary nor the proxies assume any liability as to the validity
and/or the scope of the powers of attorney presented.

The aforementioned original powers of attorney will be attached to this deed in
copies which are herewith certified.

The Notary convinced himself that the persons appearing are in adequate command
of the English language and declared that he is in command of the English
language as well.

The persons appearing stated that the parties represented by them requested that
this instrument be recorded in the English language.

On being asked whether there had been any prior involvement by the notary in
terms of paragraph 3 sub-paragraph 1 No. 7 of the German Notarisation Act
(Beurkundungsgesetz) the provisions of which had been explained by the Notary,
the persons appearing said that there had been no such prior involvement.

I.       Requesting its notarisation, the persons appearing then declared the
         following:

                                     - 3 -

<PAGE>

SHARE PLEDGE AGREEMENT
BETWEEN:

1.       Marconi Communications Holdings GmbH, a limited liability company
         organised under the laws of the Federal Republic of Germany, having its
         business address at Gerberstra(beta)e 33, D-71522 Backnang, which is
         registered in the commercial register (Handelsregister) of the local
         court (Amtsgericht) of Backnang under HRB 1562 (the "PLEDGOR"); and

2.       The Law Debenture Trust Corporation p.l.c., having its business address
         at Fifth Floor, 100 Wood Street, London, EC2V 7EX, England in its
         capacity as security trustee under the Relevant Documents (as defined
         below) (the "SECURITY TRUSTEE" or the "PLEDGEE").

WHEREAS:

(A)      Marconi Corporation p.l.c. (the "ISSUER") has agreed to issue the
         following notes:

         (i)      USD equivalent of GBP 450,000,000 senior secured notes due
                  2008 (the "SENIOR NOTES");

         (ii)     USD 300,000,000 plus USD equivalent of GBP 117,270,000 of
                  junior secured notes due 2008 (the "JUNIOR NOTES");

                  (together the "NOTES"); the notes under (i) being documented
                  in a senior note indenture dated on or about 19 May 2003
                  between, inter alios, the Issuer and Law Debenture Trust
                  Company of New York as senior note trustee and the notes under
                  (ii) being documented in a junior note indenture dated on or
                  about 19 May 2003 between, inter alios, the Issuer and
                  JPMorgan Chase Bank as junior note trustee (together the
                  "INDENTURES").

(B)      The security created by or pursuant to this Agreement is to be granted
         to and administered by the Security Trustee for itself and as trustee
         of the secured creditors pursuant to the relevant provisions of a
         security trust and intercreditor deed dated on or about 19 May 2003
         between, inter alios, the Issuer, Law Debenture Trust Company of New
         York as senior note trustee, JPMorgan Chase Bank as junior note
         trustee, the Security Trustee and the Obligors ( including the Pledgor)
         as amended from time to time (the "SECURITY TRUST AND INTERCREDITOR
         DEED").

(C)      The Pledgor has agreed to grant a first ranking pledge over its shares
         in the Company (as defined below) as security for the payment and
         discharge of the

                                     - 4 -

<PAGE>

         Secured Obligations (as defined below) subject to the terms and
         conditions set out herein.

NOW, IT IS AGREED as follows:

1.       DEFINITIONS AND LANGUAGE

1.1      In this Agreement:

         "COMPANY" means Marconi Communications ONDATA GmbH, a limited liability
         company (Gesellschaft mit beschrankter Haftung) organised under the
         laws of the Federal Republic of Germany having its business address at
         Gerberstra(beta)e 33, D-71522 Backnang, Germany, which is registered in
         the commercial register (Handelsregister) of the local court
         (Amtsgericht) of Backnang under HRB 1662.

         "CONTINUING" in relation to an Enforcement Event, shall be construed as
         a reference to an acceleration of any Obligation (other than
         Obligations arising under the New Bonding Facility Agreement) where
         such acceleration has not been rescinded in writing or a declaration
         that the Obligations (other than Obligations arising under the New
         Bonding Facility Agreement) are prematurely due and payable (other than
         solely as a result of it becoming unlawful for a secured creditor to
         perform its obligations under the Relevant Documents) where such
         declaration has not been revoked in writing or any failure by an
         Obligor to pay any principal amount in respect of any Obligations
         (other than Obligations arising under the New Bonding Facility
         Agreement) whether on maturity or otherwise which has not been waived
         in writing.

         "DEFAULT" means any event or circumstance specified as Default in any
         of the Relevant Documents (as defined below).

         "ENFORCEMENT EVENT" means the acceleration of any Obligations (as
         defined below) (other than Obligations arising under the New Bonding
         Facility Agreement (as defined below)) or any declaration that any
         Obligations (other than Obligations arising under the New Bonding
         Facility Agreement) are prematurely due and payable (other than solely
         as a result of it becoming unlawful for a secured creditor to perform
         its obligations under the Relevant Documents) or any failure by any
         Obligor to pay any principal amount in respect of any Obligations
         (other than Obligations arising under the New Bonding Facility
         Agreement) whether on maturity or otherwise.

         "ESCROW AGREEMENT" means the escrow agreement dated on or about the
         date of the Security Trust and Intercreditor Deed and made between,
         inter alia, the Security Trustee and the Issuer establishing and
         setting out the terms and conditions of each of the escrow accounts.

                                     - 5 -

<PAGE>

         "EVENT OF DEFAULT" means any event or circumstance specified as an
         Event of Default in any of the Relevant Documents (as defined below).

         "GUARANTEE" means any guarantee of any of the Obligations.

         "INITIAL SECURITY DOCUMENTS" means the Guarantees guaranteeing the
         Obligations and the security documents, each to be dated on or before
         the dates on which the Senior Notes and the Junior Notes are first
         originally issued.

         "NEW BONDING FACILITY AGREEMENT" means the GBP 50,000,000 (or the
         equivalent in other currencies) committed multicurrency revolving
         bonding facility agreement dated 27 March 2003 and entered into by,
         inter alios, the Issuer, Marconi Bonding Limited and HSBC Bank plc for
         the issuance of bonds, guarantees, letters of credit, indemnities and
         similar instruments.

         "OBLIGATIONS" means all present and future indebtedness, liabilities
         and obligations (for the avoidance of doubt, including any liabilities
         and obligations which have been cash-collateralised by the Obligors) at
         any time of any Obligor under the Relevant Documents, both actual and
         contingent and whether incurred solely or jointly or in any other
         capacity together with any of the following matters relating to or
         arising in respect of those liabilities and obligations:

         (a)      any refinancing, novation, deferral or extension;

         (b)      any obligation relating to any increase in the amount of such
                  obligations;

         (c)      any claim for damages or restitution; and

         (d)      any claim as a result of any recovery by an Obligor of a
                  payment or discharge, or non-allowability, on the grounds of
                  preference,

         and any amounts that would be included in any of the above but for any
         discharge, non-provability or unenforceability of those amounts in any
         insolvency or other proceedings (including interest accruing after the
         commencement of any insolvency or other proceedings).

         "OBLIGORS" means the Issuer, any entity being a party to the Security
         Trust and Intercreditor Deed as guarantor, including the Pledgor, and
         any entity which accedeS to the Security Trust and Intercreditor Deed
         as guarantor and an "OBLIGOR" means any of them.

         "RELEVANT DOCUMENTS" means the Security Trust and Intercreditor Deed,
         any agent/trustee accession letter relating to the Security Trust and
         Intercreditor Deed any bank accession letter relating to the New
         Bonding Facility Agreement, any guarantor accession letter relating to
         any Guarantee, the Indentures, the Escrow Agreement, the Notes, the New
         Bonding Facility Agreement, the

                                     - 6 -

<PAGE>

         Security Documents, any fee letter and any additional remuneration fee
         letter pursuant to the Security Trust and Intercreditor Deed and any
         notices issued and any other documents or agreements entered into in
         connection with or relating to such documents.

         "SECURITY DOCUMENTS" means (i) the Initial Security Documents securing
         the Obligations, (ii) any other pledge agreements, security agreements,
         mortgages, deeds of trust and other agreements, instruments and
         documents entered into from time to time by the Issuer or any
         subsidiary of the Issuer creating or granting any Guarantee, indemnity
         or security in favour of any of the secured creditors or the Security
         Trustee, as trustee for the secured creditors, as security for any of
         the Obligations and (iii) any other agreements, instruments and
         documents executed and delivered pursuant to any of the foregoing, in
         the case of each of clauses (i) through (iii), as amended, modified,
         restated or supplemented from time to time.

         "SECURED OBLIGATIONS" has the meaning given to it under Clause 3.

         "SECURITY TRUST AND INTERCREDITOR DEED" has the meaning given to it in
         Clause (B) of the recitals.

1.2      This Agreement is made in the English language. For the avoidance of
         doubt, the English language version of this Agreement shall prevail
         over any translation of this Agreement. However, where a German
         translation of a word or phrase appears in the text of this Agreement,
         the German translation of such word or phrase shall prevail.

2.       PLEDGED SHARES

2.1      The Company has a nominal share capital (Stammkapital) of EUR 1,000,000
         (in words: Euro one million) which is divided into one share, which
         share has a nominal amount of EUR 1,000,000 (in words: Euro one
         million) (the "EXISTING SHARES"). There are no other shares in the
         Company.

2.2      The Pledgor is the sole owner of the Existing Shares free from any
         encumbrances.

2.3      The Existing Shares are fully paid up. There is no obligation for the
         Pledgor to make additional contributions.

3.       SECURED OBLIGATIONS

         The pledges hereunder are constituted in order to secure together with
         other security granted by the Pledgor the prompt and complete
         satisfaction of any and all obligations (present and future, actual and
         contingent) which are (or are

                                     - 7 -

<PAGE>

         expressed to be) or become owing by the Pledgor to the Pledgee under
         the Relevant Documents (including, but not limited to the parallel
         obligations of the Pledgor pursuant to clause 3 of the Security Trust
         and Intercreditor Deed to pay to the Security Trustee sums equal to the
         sums owed by the Pledgor to the secured creditors or any of them) (the
         "SECURED OBLIGATIONS") up to an aggregate amount of EUR 200 million.

4.       PLEDGE

4.1      The Pledgor hereby pledges to the Pledgee the Existing Shares and all
         additional shares in the capital of the Company (irrespective of their
         nominal value) which the Pledgor may acquire in the future (the "FUTURE
         SHARES" and, together with the Existing Shares the "SHARES") together
         with all ancillary rights and claims associated with the Shares as more
         particularly specified in Clause 5 hereof (each a "PLEDGE" and together
         the "PLEDGES").

         The Pledgee hereby accepts the Pledges.

4.2      The validity and effect of each of the Pledges shall be independent
         from the validity and the effect of the other Pledges created
         hereunder.

4.3      Each of the Pledges is in addition, and without prejudice, to any other
         security the Pledgee may now or hereafter hold in respect of the
         Secured Obligations.

4.4      The Pledges shall rank ahead of any other security interest or third
         party right now in existence or created in the future in or over any of
         the Shares.

4.5      For the avoidance of doubt, the parties agree that nothing in this
         Agreement shall exclude a transfer of all or part of the Pledges
         created hereunder by operation of law upon the transfer or assignment
         (including by way of assumption (Vertragsubernahme)) of all or part of
         the Secured Obligations by the Pledgee to a future pledgee.

5.       SCOPE OF THE PLEDGES

5.1      The Pledges constituted by this Agreement include:

         (a)      the present and future rights to receive:

                  (i)      dividends payable in relation to the Shares, if any;
                           and

                  (ii)     liquidation proceeds, redemption proceeds
                           (Einziehungsentgelt), repaid capital in case of a
                           capital decrease, any compensation in case of
                           termination (Kundigung) and/or withdrawal (Austritt)
                           of a shareholder of the Company, the surplus in case
                           of surrender

                                     - 8 -

<PAGE>

                           (Preisgabe) and all other pecuniary claims associated
                           with the Shares;

         (b)      the right to subscribe for newly issued shares; and

         (c)      all other rights and benefits attributable to the Shares.

5.2      Notwithstanding that the dividends are pledged hereunder, the Pledgor
         shall be entitled to receive and retain, all dividend payments whether
         in cash, by the issue of any loan note or debt instrument or in specie
         in respect of the Shares until the occurrence of an Enforcement Event
         and at any time when no Enforcement Event is continuing.

6.       EXERCISE OF MEMBERSHIP RIGHTS

         The membership rights, including the voting rights, attached to the
         Shares remain with the Pledgor. The Pledgor, however, shall at all
         times until the full satisfaction of all Secured Obligations or the
         release of the Pledges exercise its membership rights, including its
         voting rights, to the extent that such exercise would not constitute a
         Default or an Event of Default.

7.       ENFORCEMENT OF THE PLEDGES

7.1      At any time after the occurrence of an Enforcement Event which is
         continuing and if the requirements set forth in Section 1204 et seq. of
         the German Civil Code (Burgerliches Gesetzbuch) with regard to the
         enforcement of any of the Pledges are met (Pfandreife), in particular,
         if any of the Secured Obligations has become due and payable, then in
         order to enforce the Pledges, the Pledgee may, in its discretion, at
         any time hereafter avail itself of all rights and remedies that a
         pledgee has upon occurrence of the requirements with regard to the
         enforcement of the Pledges under the laws of the Federal Republic of
         Germany (Pfandreife).

7.2      Notwithstanding Section 1277 of the German Civil Code, the Pledgee is
         entitled to exercise its rights without obtaining a final judgment or
         other instrument (vollstreckbarer Titel) against the Pledgor in any
         relevant court or tribunal by way of public auction.

7.3      The Pledgor hereby expressly agrees that five (5) Business Days' prior
         written notice to the Pledgor of the place and time of any such public
         auction shall be sufficient. The public auction may take place at any
         place in the Federal Republic of Germany designated by the Security
         Trustee.

7.4      If the Pledgee should seek to enforce the Pledges under this Clause
         7hereof, the Pledgor shall, at its own expense, render forthwith all
         necessary assistance in

                                     - 9 -

<PAGE>

         order to facilitate the prompt sale of the Shares or any part thereof
         and/or the exercise by the Pledgee of any other right it may have as
         Pledgee.

7.5      If the Pledges are enforced, no rights of the Pledgee shall pass to the
         Pledgor by subrogation or otherwise unless and until all of the Secured
         Obligations have been satisfied and discharged in full. In the case of
         enforcement, Section 1225 of the German Civil Code shall not apply.
         Until full discharge of the Secured Obligations, the Pledgee shall be
         entitled to treat all enforcement proceeds as additional collateral for
         the Secured Obligations, or to seek satisfaction from such proceeds at
         any time.

7.6      Following satisfaction of the requirements for enforcement under Clause
         7.1 hereof, all subsequent dividend payments and all payments based on
         similar ancillary rights attributed to the Shares may be applied by the
         Pledgee in satisfaction in whole or in part of the Secured Obligations
         or treated as additional collateral.

7.7      Even if the requirements for enforcement referred to under Clause 7.1
         above are met, the Pledgee shall not, whether as proxy or otherwise, be
         entitled to exercise the voting rights attached to the Shares.

7.8      The Pledgee may, in its sole discretion, determine which of several
         security interests, if applicable, shall be used to satisfy the Secured
         Obligations.

7.9      The Pledgor hereby expressly waives all defences of revocation (Einrede
         der Anfechtbarkeit) and set-off (Einrede der Aufrechenbarkeit) pursuant
         to Sections 770, 1211 of the German Civil Code.

7.10     With respect to the enforcement of the Pledges, the Pledgee will take
         into consideration the legitimate interest of the Pledgor.

8.       LIMITATION OF PLEDGE

8.1      The right to enforce the Pledges created hereunder shall, to the extent
         that the Secured Obligations represent those of an affiliated company
         (verbundenes Unternehmen) within the meaning of Section 15 et seq. of
         the German Stock Corporation Act (Aktiengesetz) of the Pledgor (other
         than any of the Pledgor's subsidiaries), at all times be limited to an
         amount equal to the Pledgor's assets (the calculation of which shall
         take into account the captions reflected in Section 266 sub-section (2)
         A, B and C of the German Commercial Code (Handelsgesetzbuch)) less the
         sum of (A) the Pledgor's liabilities (the calculation of which shall
         take into account the captions reflected in Section 266 subsection (3)
         B, C and D of the German Commercial Code), and (B) the stated share
         capital (Stammkapital) of the Pledgor (the "NET ASSETS").

                                     - 10 -

<PAGE>

8.2      The Pledgor shall realise, to the extent legally permitted and, in
         respect of the Pledgor, commercially justifiable, in a situation where
         the Pledgor does not have sufficient Net Assets to maintain its
         registered share capital, any and all of its assets that are shown in
         the balance sheet with a book value (Buchwert) that is significantly
         lower than the market value of the assets if the asset is not necessary
         for the Pledgor's business (betriebsnotwendig).

8.3      The Security Trustee shall enforce any Pledge created hereunder against
         the Pledgor in accordance with the following procedure:

                  (i)      The Pledgor shall, following a notification by the
                           Security Trustee to the Pledgor that an Enforcement
                           Event has occurred and that the Security Trustee
                           intends to enforce the Pledges, deliver to the
                           Security Trustee within sixty days of such
                           notification an auditors' determination from a firm
                           of auditors of international standard and reputation
                           (the "AUDITORS' DETERMINATION") stating the value of
                           the Net Assets, i.e., the amounts which may be
                           claimed against the Pledgor under the Pledges having
                           regard to Sections 30 and 31 of the German Limited
                           Liability Companies Act.

                  (ii)     The Auditors' Determination, i.e., the amount which
                           may be claimed against the Pledgor under the Pledges,
                           having regard to Section 30 and 31 of the German
                           Limited Liability Companies Act, shall take into
                           account the generally accepted accounting principles
                           applicable from time to time in Germany (GAAP) and be
                           based on the same principles that were applied when
                           establishing the previous year's balance sheet.

                  (iii)    The amount specified in the relevant Auditors'
                           Determination pertaining to the Pledgor shall be
                           up-to-date and in any event such Auditors'
                           Determination shall have been prepared as of a date
                           no earlier than 15 business days prior to the date of
                           notification by the Security Trustee to the Pledgor
                           that it intends to enforce the Pledges.

                  (iv)     If the Pledgor fails to deliver the Auditors'
                           Determination to the Security Trustee within the
                           sixty day period stated in (i) above, the Security
                           Trustee shall be entitled to enforce the Pledges
                           against the Pledgor without limitation.

9.       UNDERTAKINGS OF THE PLEDGOR

         During the term of this Agreement, the Pledgor undertakes to the
         Pledgee:

                                     - 11 -

<PAGE>

9.1      not to take, or participate in, any action which results or might
         result in the Pledgor's loss of ownership of all or part of the Shares,
         and any other transaction which would have the same result as a sale,
         transfer, encumbrance or other disposal of the Shares or which would
         for any other reason be inconsistent with the security interest of the
         Pledgee or the security purpose (as described in Clause 3 hereof)
         except, in each case, to the extent that such action is not expressly
         prohibited for the Issuer and its subsidiaries under the Indentures;
         and

9.2      insofar as additional documents, declarations or actions (including
         making all filings and registrations) are necessary for the creation,
         perfection, protection or maintenance of the Pledges created (or
         purported to be created) hereunder (or any of them) in favour of the
         Pledgee or for the exercise of all rights, powers and remedies of the
         Security Trustee provided by or pursuant to this Agreement or by law or
         to facilitate the realisation of the Pledges created (or purported to
         be created) hereunder (or any of them), the Pledgor shall at the
         Security Trustee's request, made in accordance with the Security Trust
         and Intercreditor Deed, enter into or provide such documents, make such
         declarations and undertake/or such actions at the Pledgor's cost and
         expense.

10.      EXPENSES, COSTS AND TAXES

10.1     EXPENSES

         The Pledgor shall, from time to time and promptly on demand by the
         Security Trustee reimburse to the Security Trustee all costs and
         expenses (including legal fees) on a full indemnity basis together with
         any applicable value added tax or any other tax of similar nature
         incurred by the Security Trustee and any representative, agent or
         advisor (hereinafter a "DELEGATE") (provided that in relation to
         sub-clause (i) of this Clause 10, such costs and expenses must be
         properly incurred) in connection with:

                  (i)      the execution, release and discharge of this
                           Agreement and the security created or intended to be
                           created in respect of the Pledges and the perfection
                           of the security contemplated in this Agreement or in
                           any such documents or forming part of the security
                           created or intended to be created in respect of the
                           Pledges;

                  (ii)     the actual or contemplated exercise, preservation
                           and/or enforcement of any of the rights, powers and
                           remedies of, or the performance of the duties and
                           obligations of, the Security Trustee or any Delegate,
                           or any amendment or waiver in respect of this
                           Agreement;

                  (iii)    the foreclosure of any Pledges; and

                                     - 12 -

<PAGE>

                  (iv)     the preservation and/or enforcement of the security
                           created or intended to be created in respect of the
                           Pledges,

                  which shall carry interest (before and after any judgment and
                  to the extent interest at a default rate is not otherwise
                  being paid on such sum) from the date of such demand until so
                  reimbursed calculated on a daily basis at the rate determined
                  in accordance with the provisions of clause 18.4 (Interest on
                  Demands) of the Security Trust and Intercreditor Deed.

10.2     TAXES

         The Pledgor shall pay, promptly on demand of the Security Trustee all
         stamp, registration, notarial and other similar tax, duty, levy,
         impost, assessment or other governmental charge of whatever nature
         (including penalties, interest and other liabilities related thereto)
         (hereinafter "TAXES") or fees paid or payable by the Security Trustee
         in connection with any action taken or contemplated by or on behalf of
         the Security Trustee for perfecting, enforcing, releasing, cancelling,
         reassigning or resolving any doubt concerning, or for any other purpose
         in relation to this Agreement, any amendment thereto, any transfer
         and/or assignment of the rights and/or obligations under the same or
         the security created or intended to be created in respect of the
         Pledges and shall, from time to time, indemnify the Security Trustee
         promptly on demand against any liabilities, costs, claims and expenses
         resulting from any failure to pay by the Pledgor or any delay by the
         Pledgor in paying any such Taxes or fees.

11.      DURATION AND INDEPENDENCE

11.1     This Agreement shall remain in full force and effect until complete
         satisfaction of the Secured Obligations. The Pledges shall not cease to
         exist, if the Pledgor has only temporarily discharged the Secured
         Obligations.

11.2     This Agreement shall create a continuing security and no change,
         amendment, or supplement whatsoever in the Relevant Documents or in any
         document or agreement related to any of the Relevant Documents shall
         affect the validity or the scope of this Agreement nor the obligations
         which are imposed on the Pledgor pursuant to it.

11.3     This Agreement is independent from any other security or guarantee
         which may have been or will be given to the Pledgee. None of such other
         security shall prejudice, or shall be prejudiced by, or shall be merged
         in any way with this Agreement.

                                     - 13 -

<PAGE>

12.      RELEASE (PFANDFREIGABE)

12.1     Upon complete and irrevocable satisfaction of the Secured Obligations,
         the Pledgee shall (in accordance with the terms and subject to the
         conditions and circumstances set out in the Security Trust and
         Intercreditor Deed without recourse to, or any representation or
         warranty by, the Security Trustee or any of its nominess) at the cost
         and expense of the Pledgor confirm the release of the Pledges
         (Pfandfreigabe) to the Pledgor as a matter of record. For the avoidance
         of doubt, the parties are aware that upon full and complete
         satisfaction of the Secured Obligations the Pledges, due to their
         accessory nature (Akzessorietat) cease to exist by operation of German
         law.

12.2     At any time when the total value of the aggregate security granted by
         the Pledgor to secure the Secured Obligations (the "SECURITY") which
         can be expected to be realised in the event of an enforcement of the
         Security (realisierbarer Wert) exceeds 110% of the Secured Obligations
         (the "LIMIT") not only temporarily, the Pledgee on demand of the
         Pledgor shall (in accordance with the terms and subject to the
         conditions and circumstances set out in the Security Trust and
         Intercreditor Deed without recourse to, or any representation or
         warranty by, the Security Trustee or any of its nominees) release such
         part of the Security (Sicherheitenfreigabe) as the Pledgee may in its
         reasonable discretion determine so as to reduce the realisable value of
         the Security to the Limit.

13.      PARTIAL INVALIDITY; WAIVER

13.1     If at any time, any one or more of the provisions hereof is or becomes
         invalid, illegal or unenforceable in any respect under the law of any
         jurisdiction, that provision shall as to that jurisdiction be
         ineffective to the extent necessary without affecting or impairing the
         validity, legality and enforceability of the remaining provisions of
         this Agreement or of such provisions in any other jurisdiction. The
         invalid or unenforceable provision shall be deemed replaced by a valid,
         legal and enforceable provision which comes as close as possible to the
         original intent of the parties as to the invalid, illegal or
         unenforceable provision. This shall apply analogously in the case of
         gaps.

13.2     No failure to exercise, nor any delay in exercising, on the part of the
         Pledgee, any right or remedy hereunder shall operate as a waiver
         thereof, nor shall any single or partial exercise of any right or
         remedy prevent any further or other exercise thereof or the exercise of
         any other right or remedy. The rights and remedies provided hereunder
         are cumulative and not exclusive of any rights or remedies provided by
         law.

                                     - 14 -

<PAGE>

14.      AMENDMENTS; WAIVER

         This Agreement may be amended, modified or waived only in writing
         unless notarial form by operation of law is required. This also applies
         to this Clause 14.

15.      NOTICES AND THEIR LANGUAGE

15.1     Each communication under or in connection with this Agreement shall be
         made in writing and, unless otherwise stated, may be made by fax or
         letter.

15.2     Any communication or document to be made or delivered under or in
         connection with this Agreement shall be made or delivered to the
         following addresses or fax numbers (and for the attention of the
         department or officer noted):

         For the Pledgor: Marconi Communications Holdings GmbH
                          Address:   Gerberstrasse 33
                                     D-71522 Backnang

                          Fax:       07191 13 2419
                          Attention: Hans-Werner Altermann
                                     Legal Advisor

         For the Pledgee: The Law Debenture Trust Corporation p.l.c.
                          Address:   Fifth Floor
                                     100 Wood Street
                                     London EC2V 7EX
                                     England

                          Fax:          +44 20 7696 5261
                          Attention: Manager Trust Administration

         or to such other address as the recipient may notify or may have
         notified to the other party in writing.

15.3     DELIVERY

15.3.1   Any communication or document made or delivered by one person to
         another under or in connection with this Agreement will only be
         effective:

                  (i)      if by way of fax, when received in legible form; or

                  (ii)     if by way of letter, when it has been left at the
                           address specified in Clause 15.2 above or five
                           Business Days after being deposited in the post
                           postage prepaid in an envelope addressed to the
                           addressee at that address,

                                     - 15 -

<PAGE>

         and, if a particular department or officer is specified as part of that
         address, if addressed to that department or officer.

15.3.2   Notwithstanding the provisions of sub-clause 15.3.1 (ii) above, any
         communication or document to be made or delivered to the Security
         Trustee will be effective only when actually received by the Security
         Trustee and then only if it is expressly marked for the attention of
         the department or officer identified in Clause 15.2 (or any substitute
         department or officer as such person shall specify for this purpose).

15.4     Save for the notice pursuant to Section 16 of the German Limited
         Liability Companies Act (Gesetz betreffend die Gesellschaften mit
         beschrankter Haftung) and Section 1280 of the German Civil Code
         (Burgerliches Gesetzbuch) any notice given under or in connection with
         this Agreement shall be in the English language. All other documents
         provided under or in connection with this Agreement shall be in the
         English language or, if in any other language, accompanied by a
         translation into English which if reasonably requested by the Security
         Trustee shall be a certified translation. In the event of any conflict
         between the English text and the text in any other language, the
         English text shall prevail unless the document is a constitutional,
         statutory or other official document.

16.      APPLICABLE LAW; JURISDICTION

16.1     APPLICABLE LAW

         This Agreement shall be governed by and construed in accordance with
         the laws of the Federal Republic of Germany.

16.2     GERMAN COURTS

         The courts of Frankfurt am Main have exclusive jurisdiction to settle
         any dispute (a "DISPUTE") arising out of or in connection with this
         Agreement (including a dispute regarding the existence, validity or
         termination of this Agreement or the consequences of its nullity).

16.3     CONVENIENT FORUM

         The parties agree that the courts of Frankfurt am Main are the most
         appropriate and convenient court to settle Disputes between them and,
         accordingly, that they will not argue to the contrary.

16.4     NON-EXCLUSIVE JURISDICTION

         This Clause 16 is for the benefit of the Pledgee only. As a result it
         does not prevent the Pledgee from taking proceedings relating to a
         Dispute ("PROCEEDINGS") in any other courts with jurisdiction. To the
         extent allowed by law, the Pledgee may take concurrent Proceedings in
         any number of jurisdictions.

                                     - 16 -

<PAGE>

17.      ASSIGNMENT

         The Security Trustee may assign and transfer all or any of its rights
         and obligations under this Agreement in accordance with the Security
         Trust and Intercreditor Deed. To the extent legally permissible the
         Security Trustee shall be entitled to disclose such information
         concerning the Pledgor and this Agreement as the Security Trustee
         considers appropriate to any actual or proposed direct or indirect
         successor or to any person to whom information may be required to be
         disclosed by any applicable law.

18.      EFFECTIVENESS

         This Agreement shall become effective only subject to the condition
         precedent and at the time of the first original issuance of the Senior
         Notes.

                                     - 17 -

<PAGE>

The Notary advised the persons appearing

         -        that a pledge is a security instrument of strictly accessory
                  nature (which means that it comes into legal existence only
                  if, to the extent that, and as long as, the underlying secured
                  claims do in fact exist, and that the owners of the secured
                  claims and the pledgee must be identical);

         -        that there is no bona fide creation, acquisition nor ranking
                  of a pledge of shares (which means that the pledgee is not
                  protected if the shares purported to be pledged do not exist,
                  have been previously transferred to a third party, or have
                  been previously encumbered for the benefit of a third party);
                  and

         -        that the English original version of this Agreement will not
                  be acceptable for enforcement but will have to be translated,
                  by a certified translator, into German for such purposes.

The Notary is hereby instructed to give notice of this Agreement and the Pledges
of the rights pursuant to Clause 4 (Pledge) and Clause 5 (Scope of the Pledges)
to the Company by means of forwarding to the Company a certified copy of this
Agreement.

The above Agreement including the Schedule was read aloud by the Notary to the
persons appearing, approved by them and signed in their own hand as follows:

Basel, this 15th (fifteenth) day of May, 2003 (two thousand and three)

MS MURIEL KREBS

MS STEFANIE BRENNWALD

DR THOMAS GELZER (Signed and Sealed)

Allg. Prot. Nr. 48/2003

                                     - 18 -

<PAGE>

                                    SCHEDULE
                        COPY OF SHAREHOLDERS' RESOLUTION

                                     - 19 -

<PAGE>

<TABLE>
<S>                                                                 <C>
                     GESELLSCHAFTERBESCHLUSS                                            SHAREHOLDER'S RESOLUTION
Die unterzeichnete                                                  The undersigned

                                                Marconi Communications Holdings GmbH

eingetragen im Handelsregister des Amtsgerichts Backnang unter      registered in the commercial register (Handelsregister) of the
Nr. HRB 1562                                                        Local Court (Amtsgericht) of Backnang under registration no. HRB
                                                                    1562

ist die alleinige Gesellschafterin der                              is the sole shareholder of

                                                 MARCONI COMMUNICATIONS ONDATA GmbH

eingetragen im Handelsregister des Amtsgerichts Backnang unter      registered in the commercial register (Handelsregister) of the
Nr. HRB 1662                                                        Local Court (Amtsgericht) of Backnang under registration no. HRB
                                                                    1662

                                                (die "GESELLSCHAFT" / the "COMPANY").

Die Marconi Corporation plc beabsichtigt, schuldrechtlich           Marconi Corporation plc intends to issue USD equivalent of GBP
erstrangige, garantierte und besicherte                             450,000,000.00 guaranteed and secured senior notes due 2008
Inhaberschuldver-schreibungen fallig 2008 in Hohe eines US          (referred to as "SENIOR NOTES") and USD 300,000,000.00 plus USD
Dollar Betrag, der aquivalent zu GBP 450.000.000,00 ist, (im        equivalent of GBP 117,270,000.00 guaranteed and secured Junior
folgenden "ERSTRANGIGE SCHULDVERSCHREIBUN-GEN" genannt) und USD     notes due 2008 (referred to as "JUNIOR NOTES").
300.000.000,00 plus dem aquivalenten US Dollar Betrag von GBP
117.270.000,00 schuldrechtlich zweitrangige, garantierte und
besicherte Inhaberschuldver-schreibungen fallig 2008 (im
folgenden "ZWEITRANGIGE SCHULDVERSCHREIBUNGEN" ge-nannt) zu
begeben.

Des weiteren schlossen Marconi Corporation plc, Marconi Bonding     In addition, on 27th March, 2003, Marconi Corporation plc,
Limited und andere Mitglieder der Gruppe am 27. Marz 2003 einen     Marconi Bonding Limited and other members of the Marconi group
Vertrag zur Aufnahme eines neuen Avalkredit in Hohe von GBP         entered into a GBP 50,000,000.00 new bonding facility for the
50.000.000,00, der in Form von Obligation, Burgschaften,            issuance of bonds, guarantees, letter of credits, indemnities
Akkreditiven, Garantien und ahnlichen Instrumenten ausgereicht      and similar instruments (referred to as "NEW BONDING FACILITY").
werden soll, ab (im
</TABLE>

<PAGE>

<TABLE>
<S>                                                                 <C>
folgenden "AVALKREDIT" genannt).

Unter anderem zur Besicherung (i) der Anspruche der Law             In order to secure, among others, (i) the claims of Law
Debenture Trust Company of New York als Treuhander und der          Debenture Trust Company of New York as note trustee and the
Inhaber der erstrangigen Schuldverschreibungen unter den            noteholders under the Senior Notes, (ii) the claims of JPMorgan
erstrangigen Schuldverschreibungen, (ii) der Anspruche von          Chase Bank as note trustee and the noteholders under the Junior
JPMorgan Chase Bank als Treuhander und der Inhaber der              Notes; and (iii) the claims of HSBC Bank plc as security trustee
zweitrangigen Schuldverschreibungen unter den zweitrangigen         and agent, the issuing banks and others under New Bonding
Schuldverschreibungen und (iii) der Anspruche der HSBC Bank plc     Facility, Marconi Communications Holdings GmbH intends to pledge
als Sicherheitentreuhander und Agent, der ausstellenden Banken      its present and future shares in the Company in favour of The
und anderer unter dem Avalkredit beabsichtigt Marconi               Law Debenture Trust Corporation p.l.c. as security trustee.
Communications Holdings GmbH, ihre gegen-wartigen und kunftigen
Gesellschaftsanteile an der Gesellschaft zugunsten von The Law
Debenture Trust Corporation p.l.c. als Sicherheitentreuhander zu
verpfanden.

Dies zur Kenntnis nehmend halt die unterzeichnete Marconi           Acknowledging the above the undersigned Marconi Communications
Communications Holdings GmbH als alleinige Gesellschafterin der     Holdings GmbH as sole shareholder of the Company hereby holds,
Gesellschaft hiermit unter Verzicht auf alle gesetzlichen und       waiving all and any requirements of form or notice imposed by
satzungsmassigen Frist- und Formvorschriften eine                   applicable law or the articles of the Company, a shareholders'
Gesellschaftsversammlung der Gesellschaft ab und fasst den          meeting of the Company and passes the following shareholders'
folgenden Gesellschafter-beschluss:                                 resolution:

1)   Die Marconi Communications Holdings GmbH stimmt hiermit als    1)   Marconi Communications Holdings GmbH as sole shareholder of
     alleinige Gesellschafterin der Gesellschaft der Verpfandung         the Company hereby consents to a pledge over all present
     der gegenwartigen und kunftigen Geschaftanteile an der              and future shares in the Company in favour of The Law
     Gesellschaft zugunsten von The Law Debenture Trust                  Debenture Trust Corporation p.l.c. as security trustee.
     Corporation p.l.c. als Sicherheitentreuhander zu.

2)   Die Gesellschaft des weiteren ist zum Abschlussdes globalen    2)   The Company is, furthermore, entitled to enter into the
     Lizenzvertrages                                                     global licence agreement
</TABLE>

<PAGE>

<TABLE>
<S>                                                                 <C>
     mit anderen Mitglieder der Marconi Gruppe berechtigt.               with other member of the Marconi group.

Weitere Beschlusse wurden nicht gefasst.                            No further resolutions were taken.

                                                   Backnang, den / this 14.05.2003

                                                Marconi Communications Holdings GmbH

                                                              Durch/By:

                S DICK                                                             E PROKSCHI

             Steffen Dick                                                        Edmund Prokschi

   Geschaftsfuhrer/Managing Director                                      Geschaftsfuhrer/Managing Director


                                                        M GARTNER

                                                     Michael Gartner

                                           Geschaftsfuhrer/Managing Director
</TABLE>