RNS Number:8750P
Marconi Corporation PLC
17 September 2003

The company has today received the following notification:

       Fidelity Investments
       82 Devonshire Street
       Boston, MA 0210903614


Marconi Corporation Plc
338 Euston Rd, 4th Floor
Regents Place
London NW1 3BT

Attn: Company Secretary

       September 16, 2003

Dear Sirs,

Enclosed are amended notifications of disclosable interests under the U.K.
Companies Act 1985.  Please note that while this information details the
disclosable interests of more than one entity, the enclosed disclosure
constitutes separate notifications of interests which have been combined solely
for purposes of clarity and efficiency.  It is not intended to indicate that any
of these entities act as a group or in concert with respect to these interests.

These disclosures are made in the interest of conformity with the Companies Act.
The Interest detailed herein were acquired solely for investment purposes.
For disclosure purposes, holdings should be represented as FMR Corp. and its
direct and indirect subsidiaries, and Fidelity International Limited (FIL) and
its direct and indirect subsidiaries, both being non-beneficial holders.

If you have any questions please contact Eleanor Chemlen at (617) 563-1416 or by
Fax at (617) 476-0363.



Kindest regards



Eleanor Chemlen

Sr. Compliance Specialist





Amendment #6



NOTIFICATIONS UNDER SECTIONS 198 TO 202 - U.K. COMPANIES ACT





1. Company in which shares are held:    Marconi Corporation Plc



2. Notifiable Interest:    Ordinary Shares



(A)



FMR Corp.

82 Devonshire Street

Boston, MA 02109



Parent holding company of Fidelity Management & Research Company (FMRCO),
investment manager for US mutual funds and Fidelity Management Trust Company
(FMTC), a US state chartered bank which acts as a trustee or investment manager
of various pension and trust accounts.  (See Schedule A for listing of
Registered Shareholders and their holdings.)



(B)



Fidelity International Limited (FIL)
P.O. Box HM 670

Hamilton HMCX, Bermuda



Parent holding company for various direct and indirect subsidiaries, including
Fidelity Investment Services Ltd. (FISL) and Fidelity Pension Management (FPM),
investment managers for various non-US investment companies and institutional
clients. (See Schedule A for listing of Registered Shareholders and their
holdings.)



3. The notifiable interests also comprise the notifiable interest of:



Mr. Edward C. Johnson 3d

82 Devonshire Street

Boston, MA 02109



A principal shareholder of FMR Corp. and Fidelity International Limited.



4. The notifiable interests include interest held on behalf of authorised unit
trust schemes in the U.K., notwithstanding the exemption from reporting pursuant
to Section 209 (1)(h) of the Companies Act 1985.



5. These notifications of disclosable interests constitute separate
notifications of interest in the shares and are combined solely for the purposes
of clarity and efficiency.  Nothing herein should be taken to indicate that FMR
Corp. and its direct and indirect subsidiaries, Fidelity International Limited
and its direct and indirect subsidiaries or Mr. Edward C. Johnson 3d act as a
group or in concert in respect of the disclosed interests, or that they are
required to submit these notifications on a joint basis.



6. The disclosable interests arise under section 208 (4)(b) of the Act, namely
where a person, not being the registered holder, is entitled to exercise a right
conferred by the holding of the shares or to control the exercise of such
rights, or under section 203 of the Act respectively.



                                            By: Eric D. Roiter
                                            Senior V.P & General Counsel - FMR Co
                                            Duly Authorised under Powers of Attorney
                                            dated December 30, 1997, by and on behalf
                                            of FMR Corp. and its direct and indirect
                                            subsidiaries, and Fidelity International
                                            Limited and its direct and indirect
                                            subsidiaries.


Schedule A
                           Amendment #6

Security: Marconi Corporation Plc


Ordinary Shares                   Shares Held    Management     Nominee/Registered Name
                                                   Company

                                       87,200       FMRCO       JP Morgan Chase
                                       62,563       FMRCO       State Street Bank & Trust Company
                                      865,180       FMRCO       Chase Nominees Limited
                                   14,533,160       FMRCO       HSBC
                                      364,900       FMRCO       State Street Nominees Ltd
                                       27,880       FMRCO       Citibank
                                    1,165,220       FMRCO       Brown Brothers Harriman
                                       10,460       FMTC        State Street Nominees Ltd
                                        6,840       FMTC        Mellon Bank
                                        4,880       FMTC        State Street Bank & Trust
                                    3,563,732       FISL        Chase Manhattan Bank London
                                          151       FISL        Chase Nominees Ltd
                                      185,060        FPM        Chase Nominees Ltd
                                      213,480        FIL        Chase Manhattan Bank London
                                       76,200        FIL        Northern Trust
                                      325,120        FIL        Deutsche Bank
                                       23,780        FIL        JP Morgan
                                      485,000        FIL        Brown Brothers Harriman

Total ordinary shares              22,000,800


Current ownership                     11.000%
percentage:


Shares in issue:                  200,002,000


Change in holdings               (79,710,803)
since last filing:
                              ordinary shares


                      This information is provided by RNS
            The company news service from the London Stock Exchange
END

HOLLRMATMMBBBIJ