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                                                                    EXHIBIT 4.66

                                                                  CONFORMED COPY

                                DATED 19 MAY 2003

                        (1) MARCONI COMMUNICATIONS, INC.

                 (2) THE LAW DEBENTURE TRUST CORPORATION p.l.c.
                                  (AS TRUSTEE)

--------------------------------------------------------------------------------
                         MEMORANDUM OF DEPOSIT OF SHARES
                                   AS SECURITY
--------------------------------------------------------------------------------

                            MATHESON ORMSBY PRENTICE
                                30 Herbert Street
                                    Dublin 2
                                     Ireland

                              TEL + 353 1 619 9000
                              FAX + 353 1 619 9010

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                                      INDEX

<TABLE>
<S>                                                                                              <C>
1        Interpretation.....................................................................     1

2        Covenant To Pay....................................................................     3

3        Interest...........................................................................     3

4        Deposit of Shares and Creation of Charge...........................................     4

5        Derivative Assets..................................................................     4

6        Dividends and Other Monies.........................................................     4

7        Proviso for Redemption.............................................................     5

8        Voting and Other Rights............................................................     5

9        Warranties and Undertakings........................................................     6

10       Negative Pledge....................................................................     6

11       Registration of Transfers..........................................................     6

12       Default............................................................................     6

13       Powers of Receiver.................................................................     7

14       Protection of Third Parties........................................................     7

15       Trustee Entitled To Exercise Receiver's Powers.....................................     7

16       Continuing Security................................................................     7

17       Currency Clause....................................................................     8

18       Security Additional................................................................     8

19       Consolidation......................................................................     8

20       Expenses, Costs and Taxes..........................................................     8

21       Further Assurance..................................................................     9

22       Power of Attorney..................................................................     9

23       Set Off............................................................................     10

24       Severability.......................................................................     10

25       Remedies, Waivers, Indulgence, Consents and Amendments.............................     11

26       The Trustee's Discretion...........................................................     12

27       Notices............................................................................     12

28       Assignment.........................................................................     12

29       Perpetuity Period..................................................................     12

30       Counterpart Clause.................................................................     12

31       Governing Law and Jurisdiction.....................................................     12
</TABLE>

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THIS MEMORANDUM OF DEPOSIT made on the 19th of May 2003 BY:

(1)      MARCONI COMMUNICATIONS, INC.

         having its principal place of business at 100 Marconi Drive,
         Warrendale, Pennsylvania 15086-7502, USA

         (the "Mortgagor")

IN FAVOUR OF:

(2)      THE LAW DEBENTURE TRUST CORPORATION P.L.C.

         having its head office at Fifth Floor 100 Wood Street, London EC2V 7EX,
         England (the "TRUSTEE") as security trustee for itself and the other
         Secured Creditors (as herein defined)

WITNESSES AS FOLLOWS:

1        INTERPRETATION

1.1      In this Memorandum unless the context otherwise requires:-

         "BENEFICIALLY HELD SHARES" means the 2 shares of EUR1 held by Marconi
         Networks Worldwide, Inc on behalf of the Mortgagor in the Company at
         the date hereof;

         "COMPANY" means Marconi Communications Optical Networks Limited a
         company incorporated under the laws of Ireland (Registered Number
         154999) having its registered office at West Pier Business Campus, Old
         Dunleary Road, Dun Laoire, Co Dublin;

         "CONTINUING" in relation to an Enforcement Event, shall be construed as
         a reference to an acceleration of any Secured Obligation (other than
         Secured Obligations arising under the New Bonding Facility Agreement)
         where such acceleration has not been rescinded in writing or a
         declaration that the Secured Obligations (other than Secured
         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 Secured Obligations (other than Secured
         Obligations arising under the New Bonding Facility Agreement) whether
         on maturity or otherwise which has not been waived in writing. For the
         purposes of this definition, the term "Secured Obligations" shall have
         the same meaning as in the Security Trust and Intercreditor Deed;

         "DELEGATE" means any delegate, agent, attorney, co-trustee or
         additional but separate committee, custodian, depository or receiver
         appointed by the Trustee in accordance with the terms hereof and/or the
         Security Documents;

         "DERIVATIVE ASSETS" means all stocks, shares or other securities,
         rights, monies or other property accruing, offered or issued at any
         time by way of bonus, redemption, exchange, purchase, substitution,
         conversion, preference, option or otherwise in respect of the Shares or
         in respect of any stocks, shares or other securities, rights, monies or
         other property previously accruing, offered or issued as mentioned in
         this definition;

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         "DIVIDENDS" means all dividends, interest and other income at any time
         deriving from the Shares or the Derivative Assets or deriving from any
         investment of any such dividends, interest or other income;

         "ENFORCEMENT EVENT" has the meaning given to such term in the Security
         Trust and Intercreditor Deed;

         "MORTGAGOR" includes its successors and permitted assigns (whether
         immediate or derivative);

         "SECURED ASSETS" means all assets, rights, revenues and other property
         of the Mortgagor the subject of any security created or evidenced or
         expressed or intended to be created or evidenced by or pursuant to this
         Memorandum and any reference to the "Secured Assets" includes a
         reference to any of them;

         "SECURED 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
         Mortgagor) at any time of the Mortgagor 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 the Mortgagor of a
                  payment or discharge, or non-allowability, on the grounds of
                  preference,

         and any amounts which 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);

         "SECURITY TRUST AND INTERCREDITOR DEED" means the security trust and
         intercreditor deed dated on or about the date hereof between, amongst
         others, the Trustee, Marconi Corporation plc as Issuer and other
         obligors, Law Debenture Trust Company of New York as senior note
         trustee, JPMorgan Chase Bank as junior note trustee and HSBC Bank plc
         as New Bonding Facility Agent;

         "SHARES" means the 451,392 ordinary shares of EUR 1 held by or on
         behalf of the Mortgagor in the capital of the Company at the date
         hereof together with any and all shares in the capital of the Company
         held by the Mortgagor in the future; and

         "TRUSTEE" includes any person for the time being appointed as trustee
         or as an additional trustee for the purpose of, and in accordance with,
         the Security Trust and Intercreditor Deed.

1.2      In this Memorandum:-

         1.2.1    any reference to a person shall be construed as a reference to
                  any person, firm, company, corporation, government, state or
                  agency of any government or state or any association or
                  partnership (whether or not having separate legal personality)
                  of any two or more of the foregoing;

         1.2.2    any reference to any statutory provision, order or regulation
                  shall include reference to that provision, order or regulation
                  as extended, modified, replaced or re-enacted from time to
                  time (whether before or after the date hereof) and all
                  regulations and orders from time to

                                       2

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                  time made thereunder or deriving validity therefrom and any
                  analogous provision or rule under any applicable law for the
                  time being in force;

         1.2.3    any reference to any agreement or other document shall be
                  construed as a reference to such agreement or document as
                  amended or replaced from time to time and all agreements and
                  other documents supplemental thereto;

         1.2.4    the singular shall include the plural and vice versa and the
                  masculine shall include the feminine and neuter and vice
                  versa;

         1.2.5    any reference to a clause is, unless otherwise stated, a
                  reference to a clause of this Memorandum; and

         1.2.6    headings are for reference purposes only and shall not affect
                  the interpretation of this Memorandum.

1.3      Unless otherwise defined herein, capitalised terms used herein shall
         have the meanings given to them in the Security Trust and Intercreditor
         Deed.

1.4      The parties hereto each acknowledge that the Trustee, when acting
         hereunder, shall be acting in accordance with and subject to the terms
         of the Security Trust and Intercreditor Deed.

1.5      Notwithstanding any provision to the contrary contained herein, the
         parties agree that this Memorandum is subject in all respects to the
         terms of the Security Trust and Intercreditor Deed and for the
         avoidance of doubt, in the event of any inconsistency, the provisions
         of the Security Trust and Intercreditor Deed shall prevail.

2        COVENANT TO PAY

2.1      The Mortgagor hereby covenants with the Trustee as trustee for the
         Secured Creditors that it shall on demand of the Trustee discharge all
         the Secured Obligations and shall pay to the Trustee when due and
         payable every sum at any time owing, due or incurred by it to the
         Trustee (whether for its own account or as trustee for the Secured
         Creditors) or any of the other Secured Creditors in respect of any such
         liabilities PROVIDED THAT neither such covenant nor the security
         constituted by this Memorandum nor any other provision of this
         Memorandum shall extend to or include any liability or sum which would,
         but for this proviso, cause such covenant, security or provision to be
         unlawful or prohibited by any applicable law.

2.2      All payments to be made under this Memorandum by the Mortgagor shall be
         made free and clear of and without deduction for taxes, levies,
         imposts, duties, charges or withholdings of any nature whatsoever now
         or hereafter imposed by any governmental, fiscal or other authority. If
         the Mortgagor shall at any time be compelled by law to deduct or
         withhold any amount from any payment to be made hereunder the Mortgagor
         will concurrently pay to the Trustee such additional amount as will
         result in payment to the Trustee of the full amount which would have
         been received if such deduction or withholding had not been made.

3        INTEREST

         If the Mortgagor fails to pay any sum on the due date for payment of
         that sum the Mortgagor shall pay interest on any such sum (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 demand until the
         date of payment 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.

                                       3

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4        DEPOSIT OF SHARES AND CREATION OF CHARGE

4.1      The Mortgagor hereby undertakes to deposit or cause to be deposited
         with or to the order of the Trustee within 10 Business Days after the
         date hereof the certificate relating to the Shares owned by it at the
         date hereof and deliver or cause to be delivered within 10 Business
         Days after the date hereof to or to the order of the Trustee or such
         Delegate as the Trustee may appoint for this purpose a transfer form
         duly completed by the Mortgagor and/or its nominee in respect of such
         Shares to the intent that such Shares shall henceforth be held by the
         Trustee (together with all Derivative Assets and Dividends) as trustee
         for the Secured Creditors as a continuing security for the due payment
         and discharge of the Secured Obligations.

4.2      The Mortgagor undertakes and agrees with the Trustee as trustee for the
         Secured Creditors that upon the accrual, offer or issue of any Shares
         in addition to the Shares referred to in clause 4.1 above, the
         Mortgagor will within 10 Business Days thereafter deposit with or to
         the order of the Trustee all the certificate(s) or other document(s) of
         title relating to such Shares and deliver to or to the order of the
         Trustee transfer form(s) relating to same (with the name of the
         transferee, the consideration and the date left blank, but otherwise
         duly completed), duly executed by each person in whose name such
         certificate(s) or the document(s) of title is to the intent that the
         Trustee shall hold such Shares as trustee for the Secured Creditors
         (together with all Derivative Assets and Dividends) as a continuing
         security for the due payment and discharge of the Secured Obligations.

4.3      The Mortgagor as beneficial owner hereby charges unto the Trustee as
         trustee for the Secured Creditors by way of first specific charge all
         its right, title and interest in and to the Beneficially Owned Shares,
         the Shares, the Derivative Assets and the Dividends as security for the
         payment and discharge of the Secured Obligations. The Mortgagor hereby
         agrees that upon or after (but not, for the avoidance of doubt, prior
         to) the occurrence of an Enforcement Event (which is continuing) the
         Trustee shall be at liberty at any time to cause all or any of the
         Secured Assets to be registered in the Trustee's name or in the name of
         its nominee.

5        DERIVATIVE ASSETS

         The Mortgagor undertakes and agrees with the Trustee as trustee for the
         Secured Creditors that within 10 Business Days after the accrual, offer
         or issue of any Derivative Assets the Mortgagor will deposit with or to
         the order of the Trustee or with such Delegate as the Trustee may
         approve for this purpose all certificate(s) or other document(s) of
         title relating to such Derivative Assets and, within 10 Business Days
         after any such accrual, offer or issue, deliver to or to the order of
         the Trustee or any such Delegate transfer form(s) relating to same
         (with the name of the transferee, the consideration and the date left
         blank, but otherwise duly completed) duly executed by each person in
         whose name such certificate(s) or other document(s) of title is to the
         intent the Trustee shall hold such Derivative Assets as trustee for the
         Secured Creditors as security for the Secured Obligations and such
         Derivative Assets shall be subject to the provisions of this Memorandum
         in all respects as if they formed part of the Shares.

6        DIVIDENDS AND OTHER MONIES

6.1      All Dividends and other monies forming part of the Secured Assets
         (whether of the nature of capital or income) shall, as long as no
         Enforcement Event has occurred and is continuing be paid to and
         retained by the Mortgagor and any such Dividends and other such monies
         which may be received by the Mortgagor shall, following the occurrence
         of an Enforcement Event which is continuing, be held in trust for the
         Trustee. The Trustee shall be entitled at any time following the
         occurrence of an Enforcement Event (which is continuing) to apply all
         Dividends and other such monies in or towards the reduction or
         discharge of the Secured Obligations in accordance with the provisions
         of the Security Trust and Intercreditor Deed. The Mortgagor shall,
         following the occurrence of an Enforcement Event (which is continuing),
         promptly execute and deliver (or cause

                                       4

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         to be executed and delivered) all such mandates or other authorities as
         the Trustee may require for the purpose of enabling the Trustee to
         receive all Dividends and other such monies.

6.2      The Trustee shall have no duty to ensure that any Dividends or other
         monies forming part of the Secured Assets (whether of the nature of
         capital or income) are duly and punctually paid, received or collected
         or to ensure that the correct amounts (if any) are paid.

7        PROVISO FOR REDEMPTION

7.1      The Trustee shall, at the cost of the Mortgagor, release and cancel the
         security constituted by this Memorandum and procure the reassignment to
         the Mortgagors of the property and assets assigned to the Trustee
         pursuant to this Memorandum in accordance with the terms and subject to
         the conditions and circumstances set out in the Security Trust and
         Intercreditor Deed, and without recourse to, or any representation or
         warranty by, the Trustee or any of its nominees.

7.2      A release or discharge of the Secured Assets or any of them from the
         security hereby evidenced or created may be executed by the Trustee
         alone and any such release shall be effective as if all the Secured
         Creditors had executed the same and shall be effected in accordance
         with the terms and subject to the conditions and warranties set out in
         the Security Trust and Intercreditor Deed.

8        VOTING AND OTHER RIGHTS

8.1      Before Enforcement Event

         Prior to the occurrence of an Enforcement Event and at any time when no
         Enforcement Event is continuing, the Mortgagor shall:

         8.1.1    be entitled to retain all Dividends, interest and other monies
                  arising from the Shares; and

         8.1.2    exercise all voting rights in relation to the Shares provided
                  that the Mortgagor shall not exercise such voting rights in
                  any manner which would constitute a Default or an Event of
                  Default under the Indentures (as such terms are defined in the
                  Indentures).

8.2      After Enforcement Event

         The Trustee may, upon the occurrence of an Enforcement Event and at any
         time thereafter while such an Enforcement Event is continuing, (in the
         name of the Mortgagor or otherwise and without any further consent or
         authority from the Mortgagor):

         8.2.1    exercise (or refrain from exercising) any voting rights in
                  respect of any of the Shares;

         8.2.2    apply all Dividends, interest and other monies arising from
                  any of the Shares in satisfaction of the Secured Obligations
                  in accordance with the Security Trust and Intercreditor Deed;

         8.2.3    transfer any of the Shares into the name of such nominee(s) of
                  the Trustee as it shall require; and

         8.2.4    exercise (or refrain from exercising) the powers and rights
                  conferred on or exercisable by the legal or beneficial owner
                  any of the Shares, including the right, in relation to any
                  company whose shares or other securities are included in the
                  Secured Assets, to concur or participate in:

                  (a)      the reconstruction, amalgamation, sale or other
                           disposal of such company or any of its assets or
                           undertaking (including the exchange, conversion or
                           reissue of any shares or securities as a consequence
                           thereof),

                                       5

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                  (b)      the release, modification or variation of any rights
                           or liabilities attaching to such shares or
                           securities, and

                  (c)      the exercise, renunciation or assignment of any right
                           to subscribe for any shares or securities

                  in each case in such manner and on such terms as the Trustee
                  may think fit, and the proceeds of any such action shall form
                  part of the Secured Assets.

8.3      The Mortgagor hereby irrevocably appoints the Trustee, its nominee and
         each Delegate severally its proxy so to exercise all voting and other
         rights and powers upon the occurrence of an Enforcement Event which is
         continuing so long as any of the Secured Assets remain registered in
         the name of the Mortgagor and undertakes to execute any form of proxy
         required.

9        WARRANTIES AND UNDERTAKINGS

9.1      The Mortgagor represents and warrants to the Trustee that it is the
         sole legal and beneficial owner of the Shares and the sole beneficial
         owner of the Beneficially Owned Shares free from any Security (as such
         term is defined in the Security Trust and Intercreditor Deed) except as
         created by this Memorandum.

9.2      The Mortgagor represents and warrants to the Trustee that the Shares
         are fully paid up.

10       NEGATIVE PLEDGE

         The Mortgagor shall not after the date hereof except as not expressly
         prohibited under the terms of the Indentures (a) create or permit to
         subsist any Security over the Secured Assets or (b) permit any person
         other than the Mortgagor, the Trustee, the Trustee's nominee, or any
         Delegate any receiver appointed hereunder or any purchaser from the
         Trustee or any such receiver to be registered as holder of the Secured
         Assets or any of them.

11       REGISTRATION OF TRANSFERS

         The Mortgagor shall take all steps within its power or procurement to
         procure that any transfer of any of the Secured Assets to the Trustee
         or its nominee or any Delegate or any receiver appointed hereunder or
         to any purchaser from the Trustee or such a Delegate or such receiver
         on a realisation of the security hereby evidenced or created shall be
         registered by the directors of the Company.

12       DEFAULT

         At any time after the occurrence of an Enforcement Event (which is
         continuing) the security evidenced and created by this Memorandum shall
         become enforceable and the Trustee (acting on instructions received
         pursuant to the terms of the Security Trust and Intercreditor Deed) may
         forthwith or at any time thereafter upon giving notice to the Mortgagor
         (i) sell all or any of the Secured Assets in any manner permitted by
         law upon such terms as the Trustee in its absolute discretion shall
         determine and in relation to any such sale the provisions of the
         Conveyancing Acts, 1881 to 1911 shall apply but without the
         restrictions contained in Section 20 of the Conveyancing Act, 1881;
         and/or (ii) collect, recover or compromise and give a good discharge
         for any moneys payable in respect of the Secured Assets or in
         connection therewith and/or (iii) by instrument in writing appoint any
         person to be a receiver of all or any part of the Secured Assets and
         may in like manner remove any such receiver and appoint another in his
         stead.

                                       6

<PAGE>

13       POWERS OF RECEIVER

13.1     Any receiver appointed hereunder upon the occurrence of an Enforcement
         Event (which is continuing), shall, in addition to any powers conferred
         on him by virtue of the Conveyancing Acts, 1881 to 1911, have power
         from time to time (i) to take possession of, collect and get in all or
         any of the Secured Assets and for this purpose to enter upon any
         property of the Mortgagor; (ii) to carry on or concur in carrying on
         the business of the Mortgagor; (iii) to settle, adjust, refer to
         arbitration, arrange or compromise any claims, accounts, disputes,
         questions and demands relating in any way to the Secured Assets which
         he may think expedient; (iv) to bring, prosecute, enforce, defend and
         abandon actions, suits and proceedings in relation to the Secured
         Assets; (v) to sell or realise or concur in selling or realising all or
         any of the Secured Assets upon any terms which such receiver shall
         think reasonable (for which purpose the Mortgagor hereby irrevocably
         appoints every receiver appointed hereunder to be the attorney of the
         Mortgagor); (vi) for the purpose of exercising any of the rights,
         powers or authorities conferred on any receiver appointed hereunder to
         borrow or raise money either unsecured or on the security of the
         Secured Assets (either in priority to the security hereby evidenced or
         created) and generally on such terms and conditions as he may think
         fit; and (vii) to do all such other acts and things as he may consider
         desirable or necessary for realising the Secured Assets or any of them
         or conducive to any of the matters, powers or authorities conferred on
         any receiver appointed hereunder by this Memorandum or by law and to
         exercise in relation to the Secured Assets or any of them all such
         powers, authorities and things as he would be capable of exercising if
         he were the absolute beneficial owner of the same and to use the name
         of the Mortgagor for all or any of the purposes aforesaid.

13.2     Every receiver appointed hereunder shall be the agent of the Mortgagor
         and the Mortgagor shall be solely responsible for his acts or defaults
         and for his remuneration.

13.3     Any monies received by the Trustee or by any receiver shall, after the
         security hereby constituted has become enforceable but subject to the
         payment of any claims having priority to this security, be applied in
         accordance with the terms of the Security Trust and Intercreditor Deed.

14       PROTECTION OF THIRD PARTIES

14.1     No purchaser or other person dealing with the Trustee, any Delegate or
         any receiver appointed hereunder shall be bound or concerned to see or
         enquire whether the right of the Trustee, any Delegate or any such
         receiver to exercise any of the powers hereby conferred has arisen or
         has become exercisable or be concerned with the propriety of the
         exercise or purported exercise of such powers.

14.2     The receipt of the Trustee, any Delegate or any receiver appointed
         hereunder shall be an absolute and conclusive discharge to a purchaser
         or other person dealing with the Trustee or such Delegate or receiver
         and shall relieve him of any obligation to see to the application of
         any monies paid to or by the direction of the Trustee or such Delegate
         or such receiver.

15       TRUSTEE ENTITLED TO EXERCISE RECEIVER'S POWERS

         All or any of the powers, authorities and discretions which are
         conferred by this Memorandum (either expressly or impliedly) upon any
         receiver may be exercised after the security hereby evidenced or
         created has become enforceable by the Trustee in relation to the whole
         of the Secured Assets or any part thereof without first appointing a
         receiver of the Secured Assets or any part thereof or notwithstanding
         the appointment of a receiver of the Secured Assets or any part
         thereof.

16       CONTINUING SECURITY

16.1     The security hereby evidenced and created shall constitute and be a
         continuing security and shall not be considered satisfied by any
         intermediate payment or satisfaction of all or any of the Secured

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         Obligations and shall continue in full force and effect until all the
         Secured Obligations have been discharged in full.

16.2     If the Trustee or any Secured Creditor shall at any time receive notice
         of any subsequent mortgage, assignment, charge or other interest
         affecting all or any of the Secured Assets, the Trustee or that Secured
         Creditor (as the case may be) shall be entitled to open a new account
         or accounts for the Mortgagor in its books and if the Trustee or that
         Secured Creditor (as the case may be) does not in fact do so then
         (unless the Trustee or that Secured Creditor (as the case may be) gives
         express written notification to the Mortgagor that it has not done so)
         as from the time when the Trustee or that Secured Creditor (as the case
         may be) received such notice all payments made by the Mortgagor to the
         Trustee or that Secured Creditor (as the case may be) shall be treated
         as having been credited to such new account of the Mortgagor and not as
         having been applied in reduction of the Secured Obligations outstanding
         at the time of receipt of such notice by the Trustee or that Secured
         Creditor (as the case may be).

17       CURRENCY CLAUSE

         If any sum (a "SUM") owing by the Mortgagor under this Memorandum or
         any order or judgment given or made in relation to this Memorandum has
         to be converted from the currency (the "FIRST CURRENCY") in which such
         Sum is payable into another currency (the "SECOND CURRENCY") for the
         purpose of:

         (a)      making or filing a claim or proof against the Mortgagor;

         (b)      obtaining an order or judgment in any court or other tribunal;

         (c)      enforcing any order or judgment given or made in relation to
                  this Memorandum; or

         (d)      applying the Sum in satisfaction of any of the Secured
                  Obligations,

         the Mortgagor shall indemnify the Trustee from and against any loss
         suffered or incurred as a result of any discrepancy between (a) the
         rate of exchange used for such purpose to convert such Sum from the
         First Currency into the Second Currency and (b) the rate or rates of
         exchange available to the Trustee at the time of such receipt of such
         Sum.

18       SECURITY ADDITIONAL

         This Memorandum and the security hereby evidenced and created shall be
         in addition to and shall not be affected by any other mortgage charge
         pledge lien or other security or guarantee or indemnity which the
         Trustee or any Secured Creditor may at any time hold for any of the
         Secured Obligations. No other mortgage charge pledge lien or other
         security or guarantee or indemnity now or hereafter held by the Trustee
         or any Secured Creditor over the Secured Assets shall merge in the
         security created by this Memorandum.

19       CONSOLIDATION

         The restriction on the right of consolidating mortgages contained in
         Section 17 of the Conveyancing Act, 1881 shall not apply in relation to
         this Memorandum.

20       EXPENSES, COSTS AND TAXES

20.1     EXPENSES

         The Mortgagor shall, from time to time and promptly on demand by the
         Trustee reimburse the Trustee in respect of all costs and expenses
         (including legal fees) on a full indemnity basis together

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<PAGE>

         with any applicable VAT incurred by the Trustee and any Delegate
         (PROVIDED THAT in relation to sub-clause 20.1.1 of this clause 20.1,
         such costs and expenses must be properly incurred) in connection with:

         20.1.1   the execution, release and discharge of this Memorandum and
                  the Security created or intended to be created in respect of
                  the Secured Assets and the perfection of the Security
                  contemplated in this Memorandum or in any such documents or
                  forming part of the Security created or intended to be created
                  in respect of the Secured Assets;

         20.1.2   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 Trustee
                  or any Delegate, or any amendment or waiver in respect of this
                  Memorandum;

         20.1.3   the preservation and/or enforcement of the Security created or
                  intended to be created in respect of the Secured Assets; and

         20.1.4   the foreclosure of any Secured Assets,

         which shall carry interest from the date of such demand until so
         reimbursed at the rate and on the basis as mentioned in clause 3.

20.2     TAXES

         The Mortgagor shall pay promptly on demand of the Trustee all stamp,
         registration, notarial and other similar taxes or fees paid or payable
         by the Trustee in connection with any action taken or contemplated by
         or on behalf of the Trustee for perfecting, enforcing, releasing,
         cancelling, reassigning or resolving any doubt concerning, or for any
         other purpose in relation to this Memorandum, 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 Secured Assets and shall, from time to time, indemnify the
         Trustee promptly on demand against any liabilities, costs, claims and
         expenses resulting from any failure to pay by the Mortgagor or any
         delay by the Mortgagor in paying any such taxes or fees.

21       FURTHER ASSURANCE

         The Mortgagor shall promptly do all such acts or execute all such
         documents (including assignments, transfers, mortgages, charges,
         notices and instructions) as the Trustee may specify (and in such form
         as the Trustee may require in favour of the Trustee or its nominee(s)):

         (a)      to perfect the Security created or intended to be created in
                  respect of the Secured Assets (which may include the execution
                  by the Mortgagor of a mortgage, charge or assignment over all
                  or any of the assets constituting, or intended to constitute,
                  Secured Assets) or for the exercise of any rights relating
                  thereto;

         (b)      to confer on the Trustee Security over any property and assets
                  of that Company located in any jurisdiction outside Ireland
                  equivalent or similar to the Security intended to be conferred
                  by or pursuant to this Memorandum; and/or

         (c)      to facilitate the realisation of the Secured Assets.

22       POWER OF ATTORNEY

22.1     The Mortgagor hereby irrevocably and by way of security appoints the
         Trustee, each Delegate and separately any receiver severally to be its
         attorney (the "Attorney") in its name and on its behalf and as its act
         and deed or otherwise to:-

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         22.1.1   following the occurrence of an Enforcement Event (which is
                  continuing) execute, complete and perfect in favour of the
                  Trustee or its nominees or of any purchaser or any Delegate
                  any documents which the Trustee may require for perfecting its
                  title to or for vesting the Secured Assets in the Trustee or
                  its nominees or in any purchaser or any Delegate;

         22.1.2   execute, complete and perfect all documents and do all such
                  acts and things as may be required for the full exercise of
                  all or any of the powers hereby conferred or which may be
                  deemed expedient by the Trustee, any Delegate or any receiver
                  on or in connection with any sale, lease, disposition,
                  realisation or getting in by the Trustee or any receiver of
                  the Secured Assets or any part thereof or in connection with
                  any other exercise of any power hereunder; and

         22.1.3   execute, deliver and perfect all documents and do all things
                  which the Trustee, any Delegate or any receiver may consider
                  to be required or desirable for:

                  (i)      carrying out any obligation imposed on the Mortgagor
                           by this Memorandum (including the execution and
                           delivery of any notices, deeds, charges, assignments
                           or other security and any transfers of the Secured
                           Assets); and

                  (ii)     enabling the Trustee, each Delegate or any receiver
                           to exercise, or delegate the exercise of, any of the
                           rights, powers and authorities conferred on them by
                           or pursuant to this Memorandum or by law (including,
                           after the occurrence of an Enforcement Event (which
                           is continuing), the exercise of any right of a legal
                           or beneficial owner of the Secured Assets).

         The Mortgagor hereby covenants with the Trustee, each Delegate and
         separately with any receiver that on request it will ratify and confirm
         all security agreements, documents, acts and things and all
         transactions done and entered into by the Trustee, any Delegate or any
         receiver or by the Mortgagor at the instance of the Trustee, any
         Delegate or any receiver in the exercise or purported exercise of its
         or his powers.

22.2     Each of the Trustee and any receiver shall have full power to delegate
         the power conferred on it or him by this clause 22 but no such
         delegation shall preclude the subsequent exercise of such power by the
         Trustee or the receiver itself or himself or preclude the Trustee or
         the receiver from making a subsequent delegation thereof to some other
         person; any such delegation may be revoked by the Trustee or the
         receiver at any time.

22.2     The Mortgagor shall indemnify the Attorney and keep the Attorney
         indemnified against any and all costs, claims and liabilities which the
         Attorney may incur as a result of anything done by the Attorney in the
         proper exercise of any of the powers conferred, or purported to be
         conferred, on him or her by this Memorandum unless such cost, claim or
         liability arises as a result of the negligence or wilful misconduct of
         the Attorney.

23       SET OFF

         The Mortgagor authorises the Trustee (but the Trustee shall not be
         obliged to exercise such right), after the occurrence of an Enforcement
         Event which is continuing, to set off against the Secured Obligations
         any amount or other obligation (contingent or otherwise) owing by the
         Trustee to the Mortgagor.

24       SEVERABILITY

         Each of the provisions of this Memorandum is severable and distinct
         from the others and if at any time any such provision is or becomes
         invalid illegal or unenforceable in any jurisdiction that shall not
         affect the validity legality or enforceability of the remaining
         provisions hereof or affect the

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         validity legality or enforceability of such provision in any other
         jurisdiction. Without prejudice to the foregoing, if at any time any
         liability in relation to the Secured Obligations is or becomes invalid,
         illegal or unenforceable then such occurrence shall not prejudice the
         continuing effectiveness of the security evidenced or created by this
         Memorandum for any liability in relation to the Secured Obligations
         which is not so affected.

25       REMEDIES, WAIVERS, INDULGENCE, CONSENTS AND AMENDMENTS

25.1     The rights, powers and remedies provided in this Memorandum are
         cumulative and not, nor are they to be construed as, exclusive of any
         rights, powers or remedies provided by law or otherwise.

25.2     No failure or delay by the Trustee or any Secured Creditor in
         exercising any right or remedy shall operate as a waiver thereof nor
         shall any single or any partial exercise or waiver of any right or
         remedy preclude its further exercise or the exercise of any other right
         or remedy.

25.3     Any provision of this Memorandum may be amended, supplemented or
         novated only if the Mortgagor and the Trustee so agree in writing. Any
         waiver of, and any consent or approval by the Trustee under any
         provision of this Memorandum shall not be effective unless it is in
         writing, and may be given subject to any conditions thought fit by the
         Trustee, may be withdrawn or modified at any time and shall be
         effective only in the instance and for the purpose for which it was
         given.

25.4     The liability of the Mortgagor hereunder will not be affected by any
         act, omission, circumstances, matter or thing which but for this
         provision would release or prejudice any of its obligations hereunder
         or prejudice or diminish such obligation in whole or in part, including
         without limitation and whether or not known to the Mortgagor, or the
         Trustee or any Secured Creditor or any other person whatsoever:

         25.4.1   any winding-up, dissolution, examinership, administration or
                  re-organisation of or other change in any Mortgagor or any
                  other person;

         25.4.2   any of the Secured Obligations being at any time illegal,
                  invalid, unenforceable or ineffective;

         25.4.3   any time or other indulgence being granted to any Mortgagor or
                  any other person;

         25.4.4   any amendment, variation, waiver or release of any of the
                  Secured Obligations;

         25.4.5   any failure to take or failure to realise the value of any
                  other collateral in respect of the Secured Obligations or any
                  release, discharge, exchange or substitution of any such
                  collateral;

         25.4.6   any other act, event, or omission which but for this provision
                  would or might operate to impair, discharge or otherwise
                  affect the obligations of any Mortgagor hereunder.

25.5     Neither the Trustee, the Secured Creditors nor any receiver appointed
         hereunder shall be under any liability for loss of any kind (including,
         without limitation, any loss arising from changes in exchange rates or
         the diminution in the value of any of the Secured Assets) which may be
         occasioned by the exercise or purported exercise of, or any delay or
         neglect to exercise any of its rights under or pursuant to this
         Memorandum (except in the case of negligence or wilful default on its
         part) and in particular without limitation neither the Trustee, the
         Secured Creditors nor any receiver appointed hereunder shall (except in
         the case of negligence or wilful default on its part) be liable to
         account as mortgagee in possession or for anything except actual
         receipts.

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26       THE TRUSTEE'S DISCRETION

26.1     Any liberty or power which may be exercised or any determination which
         may be made hereunder by the Trustee may be exercised or made in the
         absolute and unfettered discretion of the Trustee which shall not be
         under any obligation to give reasons therefor.

27       NOTICES

27.1     Each communication to be made under this Memorandum shall be made and
         delivered in accordance with the provisions of the Security Trust and
         Intercreditor Deed.

28       ASSIGNMENT

28.1     This Memorandum shall be binding upon and inure to the benefit of each
         party hereto and its successors personal representatives and permitted
         assigns.

28.2     The Trustee and any Secured Creditor may assign or transfer all or any
         of its rights and obligations hereunder in accordance with the Security
         Trust and Intercreditor Deed. The Trustee and any Secured Creditor
         shall be entitled to impart any information concerning the Mortgagor
         and this Memorandum as the Trustee considers appropriate to any actual
         or purported assignee, transferee or other successor or any
         participant.

29       PERPETUITY PERIOD

         The perpetuity period under the rule against perpetuities, if
         applicable to this Memorandum, shall be the period of eighty years from
         the date of the Security Trust and Intercreditor Deed.

30       COUNTERPART CLAUSE

         This Memorandum may be executed in counterparts and by the parties on
         separate counterparts each of which when executed and delivered shall
         together constitute one and the same instrument.

31       GOVERNING LAW AND JURISDICTION

31.1     This Memorandum shall be governed by and construed in accordance with
         the Laws of Ireland.

31.2     It is irrevocably agreed for the exclusive benefit of the Trustee and
         each Secured Creditor that the courts of Ireland are to have
         jurisdiction to settle any disputes which may arise out of or in
         connection with this Memorandum and that accordingly any suit, action
         or proceeding arising out of or in connection with this Memorandum (in
         this clause referred to as "Proceedings") may be brought in such
         courts. Nothing in this clause shall limit the right of the Trustee or
         any Secured Creditor to take Proceedings against the Mortgagor in any
         other court of competent jurisdiction, nor shall the taking of
         Proceedings in one or more jurisdictions preclude the taking of
         Proceedings in any other jurisdiction, whether concurrently or not.

31.3     The Mortgagor hereby irrevocably authorises and appoints Marconi
         Communications Optical Networks Limited (or such other person, being a
         firm of solicitors resident in Ireland as it may by notice to the other
         parties hereto substitute) to accept service of all legal process
         arising out of or connected with this Memorandum and service on Marconi
         Communications Optical Networks Limited (or such substitute) shall be
         deemed to be service on such party.

IN WITNESS whereof the Mortgagor has duly executed this Memorandum on the 19th
of May 2003

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SIGNED SEALED AND DELIVERED                                          CARLA MORAN
by the authorised attorney of
THE MORTGAGOR
in the presence of:

Witness Signature:         H MARREN

Witness name:              HILARY MARREN

Witness Address:           2 Harbourmaster Place, IFSC, Dublin 1

EXECUTED AS A DEED
on behalf of THE TRUSTEE by:-                        J. M. JEBB
                                                     Director

                                                     R. D. RANCE
                                                     Director

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