Rule 8.3 - MARCONI CORPORATION PLC

FORM 8.3

DEALINGS BY PERSONS WHO OWN OR CONTROL 1% OR MORE OF ANY CLASS OF RELEVANT SECURITY
(Rule 8.3 of The City Code on Takeovers and Mergers)

Name of purchaser/vendor *                         BARCLAYS PLC
Company dealt in                                   MARCONI CORPORATION PLC
Relevant security dealt in                         ORD GBP 0. 25
If a connected EFM, name of offeree/offeror with
which connected
If a connected EFM, nature of connection #
Date of dealing                                    08 AUGUST 2005

DEALINGS †

Amount bought                               Price per unit  (currency must be stated)
3,788                                       Transfer
23,190                                      3.0496


Amount sold                                 Price per unit (currency must be stated)
20,478                                      2.9091
22,658                                      3.0712
4,200                                       3.0300


Resultant total amount and percentage of the
same relevant security owned or controlled  9,275,402 (4.44%)

IS A SUPPLEMENTAL FORM 8 (DERIVATIVE)/FORM 8 (OPTION) ATTACHED? YES

Date of disclosure   09 AUGUST 2005
Contact name         BARCLAYS CORPORATE SECRETARIAT
Telephone number     0207 116 2913

* Specify the owner or controller in addition to the person dealing. The naming of nominees or
vehicle companies is insufficient.

In the case of disclosure of dealings by fund managers on behalf of discretionary clients,
the clients need not be named.

# See the definition of "connected fund managers and principal traders" in the Definitions
Section of the Code.

† If disclosing dealings/holdings in derivatives or options, please attach Supplemental Form 8 (Derivative) or
Supplemental Form 8 (Option), as appropriate.

SUPPLEMENTAL FORM 8 (DERIVATIVE)

For details of the Code's dealing disclosure requirements, see Rule 8 and its Notes which can be viewed on the Takeover
Panel's website at www.thetakeoverpanel.org.uk.


DEALINGS/HOLDINGS IN DERIVATIVES
(This form should be attached to Form 8.1, Form 8.1(b)(ii), Form 8.2 or Form 8.3, as appropriate)

Description of all derivative products       CFD - A purchaser of a CFD will realise
disclosed on this form                       a gain if the price of the underlying security
                                             goes up. A seller of a CFD will realise a gain
                                             if the price of the underlying security goes down.
                                             The CFD contracts are open ended and there is no
                                             rollover into new contracts.


Full details of any agreement, arrangement   None
or understanding between the person
disclosing and any other person relating
to the voting rights or future acquisition
or disposal of any relevant securities to
which any derivative referred to on this
form is referenced. If none, this should
be stated.


WRITING/ENTERING INTO A DERIVATIVE

Product name   Transaction    Writing/        Number of        Reference price   Maturity date
eg long CFD    date           entering into   securities       (currency
                              (indicate as    to which the     must be stated)
                              applicable)     derivative
                                              is referenced
Long CFD       08/08/2005     Written         20,478           2.9091
Long CFD       08/08/2005     Written         22,658           3.0712
Long CFD       08/08/2005     Written         4,200            3.0300
Short CFD      08/08/2005     Written         23,190           3.0496
Short CFD      08/08/2005     Entered into    14,874           2.9106
Short CFD      08/08/2005     Entered into    4,912            2.9106
Short CFD      08/08/2005     Entered into    20,478           2.9106

CLOSING OUT A DERIVATIVE

Product name   Transaction    Number of        Reference price   Closing out price
eg long CFD    date           securities       (currency         (currency must be
                              to which the     must be stated)   stated)
                              derivative
                              is referenced


DETAILS OF OPEN DERIVATIVES (excluding any transaction set out above)

Product name   Transaction    Written/        Number of          Reference price   Maturity date
eg long CFD    date           entered into    securities         (currency
                              (indicate as    to which the       must be stated)
                              applicable)     derivative
                                              is referenced
Short CFD      09/06/2004     Entered into    32,136             6.8435
Long CFD       21/06/2004     Entered into    19,380             6.4508
Short CFD      28/07/2004     Entered into    17,847             6.1389
Short CFD      28/07/2004     Entered into    42,082             6.1389
Short CFD      06/08/2004     Entered into    17,078             5.9840
Short CFD      06/08/2004     Entered into    27,038             5.9840
Long CFD       23/08/2004     Entered into    8,621              5.8400
Long CFD       01/09/2004     Entered into    8,636              5.8150
Short CFD      27/09/2004     Entered into    14,492             5.8623
Long CFD       05/10/2004     Entered into    18,232             5.9582
Short CFD      11/10/2004     Entered into    50,155             5.8542
Short CFD      13/10/2004     Entered into    8,216              5.8000
Short CFD      15/10/2004     Entered into    15,677             5.1500
Short CFD      15/10/2004     Entered into    137,517            5.1500
Short CFD      27/10/2004     Entered into    12,411             5.1997
Short CFD      02/11/2004     Entered into    19,011             5.1732
Short CFD      18/11/2004     Entered into    8,803              5.8250
Short CFD      24/11/2004     Entered into    40,703             5.6863
Short CFD      26/11/2004     Entered into    53,784             5.7742
Short CFD      01/12/2004     Entered into    24,432             5.6848
Long CFD       13/12/2004     Entered into    269,548            5.6300
Short CFD      14/12/2004     Entered into    121,173            5.5650
Short CFD      10/01/2005     Entered into    21,988             5.7300
Short CFD      12/01/2005     Entered into    20,353             5.8500
Short CFD      17/01/2005     Entered into    42,156             5.9900
Short CFD      19/01/2005     Entered into    32,665             5.9580
Short CFD      25/01/2005     Entered into    25,527             5.8196
Long CFD       01/02/2005     Entered into    46,447             6.2963
Long CFD       03/02/2005     Entered into    11,680             6.1475
Long CFD       09/02/2005     Entered into    12,240             5.7364
Short CFD      11/02/2005     Entered into    17,250             5.7678
Short CFD      22/02/2005     Entered into    15,713             5.6350
Short CFD      25/02/2005     Entered into    9,361              5.7004
Short CFD      28/02/2005     Entered into    10,848             5.6975
Short CFD      01/03/2005     Entered into    8,811              5.7542
Short CFD      03/03/2005     Entered into    8,826              5.7172
Short CFD      14/03/2005     Entered into    21,841             5.6226
Short CFD      16/03/2005     Entered into    80,076             5.5325
Short CFD      21/03/2005     Entered into    13,709             5.6100
Short CFD      04/04/2005     Entered into    17,467             5.4346
Short CFD      04/04/2005     Entered into    37,720             5.4346
Short CFD      19/04/2005     Entered into    5,904              5.1374
Short CFD      20/04/2005     Entered into    6,653              5.1337
Short CFD      09/05/2005     Entered into    153,353            2.7575
Short CFD      20/05/2005     Entered into    136,929            2.8550
Short CFD      26/05/2005     Entered into    74,783             2.9639
Short CFD      01/06/2005     Entered into    21,697             2.9600
Short CFD      01/06/2005     Entered into    26,317             2.9600
Short CFD      01/06/2005     Entered into    69,107             2.9556
Short CFD      07/06/2005     Entered into    18,747             3.0050
Short CFD      10/06/2005     Entered into    929                3.1300
Short CFD      27/06/2005     Entered into    6,280              3.0400
Short CFD      27/06/2005     Entered into    2,237              3.0400
Short CFD      27/06/2005     Entered into    12,106             3.0400
Short CFD      28/06/2005     Entered into    57,825             3.0319
Short CFD      28/06/2005     Entered into    20,611             3.0319
Short CFD      28/06/2005     Entered into    111,446            3.0319
Short CFD      29/06/2005     Entered into    727                3.0100
Short CFD      29/06/2005     Entered into    190                3.0100
Short CFD      29/06/2005     Entered into    1,112              3.0100
Short CFD      30/06/2005     Entered into    60,466             3.0400
Short CFD      30/06/2005     Entered into    15,824             3.0400
Short CFD      30/06/2005     Entered into    92,332             3.0400
Short CFD      01/07/2005     Entered into    52,119             3.0320
Short CFD      01/07/2005     Entered into    17,474             3.0320
Short CFD      05/07/2005     Entered into    6,022              2.9602
Short CFD      05/07/2005     Entered into    1,160              2.9602
Short CFD      06/07/2005     Entered into    75,585             2.9550
Short CFD      06/07/2005     Entered into    14,584             2.9550
Short CFD      15/07/2005     Entered into    60,041             2.8013
Short CFD      18/07/2005     Entered into    18,943             2.8398
Short CFD      22/07/2005     Entered into    27,706             2.6682
Short CFD      22/07/2005     Entered into    11,644             2.6681
Short CFD      26/07/2005     Entered into    27,298             2.7334
Short CFD      26/07/2005     Entered into    11,199             2.7334
Short CFD      26/07/2005     Entered into    46,803             2.7380
Short CFD      03/08/2005     Entered into    1,769              2.7040
Short CFD      03/08/2005     Entered into    1,364              2.7040
Short CFD      04/08/2005     Entered into    16,513             2.6538
Short CFD      04/08/2005     Entered into    12,746             2.6537
Short CFD      05/08/2005     Entered into    3,428              2.6721
Short CFD      05/08/2005     Entered into    1,132              2.6721
Short CFD      05/08/2005     Entered into    5,074              2.6746