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                                    12 OCTOBER 2005

DEALINGS †

Amount bought                               Price per unit  (currency must be stated)
39,588                                      3.3248
8,800                                       3.3615

Amount sold                                 Price per unit (currency must be stated)
8,500                                       3.3800
75,000                                      3.3700
428,039                                     3.3802
1,940,000                                   3.3903
12,000                                      3.3393
11,700                                      3.3475

Resultant total amount and percentage of the
same relevant security owned or controlled  1,979,734 (0.94%)

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

Date of disclosure   13 OCTOBER 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      12/10/2005      Written         12,000           3.3393
Long CFD      12/10/2005      Written         11,700           3.3475
Short CFD     12/10/2005      Written         8,800            3.3615

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      19/01/2004     Written         600                7.1059
Short CFD      27/01/2004     Written         700                6.7724
Short CFD      28/01/2004     Written         6,300              6.5787
Long CFD       29/01/2004     Written         2,500              6.4492
Long CFD       30/01/2004     Written         4,100              6.6055
Long CFD       02/02/2004     Written         5,800              6.6748
Long CFD       04/02/2004     Written         2,100              6.5892
Long CFD       11/02/2004     Written         700                7.1441
Short CFD      16/02/2004     Written         2,700              6.9927
Short CFD      20/02/2004     Written         1,600              7.1909
Short CFD      11/03/2004     Written         3,300              6.4297
Short CFD      16/03/2004     Written         19,500             6.1113
Long CFD       26/03/2004     Written         1,300              6.5492
Long CFD       08/04/2004     Written         10,700             6.7970
Long CFD       13/04/2004     Written         500                6.7942
Short CFD      21/04/2004     Written         14,400             6.5816
Short CFD      28/04/2004     Written         6,500              6.0996
Short CFD      29/04/2004     Written         32,000             5.9769
Short CFD      30/04/2004     Written         9,700              5.8850
Short CFD      10/05/2004     Written         40,400             5.3440
Short CFD      11/05/2004     Written         8,600              5.5416
Long CFD       18/05/2004     Written         8,300              5.7400
Long CFD       19/05/2004     Written         36,700             6.1167
Long CFD       25/05/2004     Written         700                6.1343
Long CFD       26/05/2004     Written         12,100             6.2820
Long CFD       27/05/2004     Written         10,300             6.3064
Long CFD       28/05/2004     Written         30,300             6.4978
Long CFD       01/06/2004     Written         20,900             6.5733
Short CFD      09/06/2004     Entered into    32,136             6.8435
Short CFD      16/06/2004     Written         700                6.5858
Long CFD       21/06/2004     Entered into    19,380             6.4508
Short CFD      01/07/2004     Written         8,300              6.7642
Short CFD      08/07/2004     Written         500                6.6458
Short CFD      09/07/2004     Written         2,900              6.6542
Short CFD      15/07/2004     Written         35,500             6.3959
Short CFD      16/07/2004     Written         43,000             6.5073
Short CFD      22/07/2004     Written         25,200             6.3378
Short CFD      28/07/2004     Written         20,100             6.1352
Short CFD      28/07/2004     Entered into    17,847             6.1389
Short CFD      28/07/2004     Entered into    42,082             6.1389
Long CFD       06/08/2004     Written         22,900             6.0451
Short CFD      06/08/2004     Entered into    17,078             5.9840
Short CFD      06/08/2004     Entered into    27,038             5.9840
Short CFD      11/08/2004     Written         13,600             5.4670
Long CFD       23/08/2004     Entered into    8,621              5.8400
Long CFD       01/09/2004     Entered into    8,636              5.8150
Long CFD       10/09/2004     Written         1,100              6.1043
Short CFD      16/09/2004     Written         25,367             6.0255
Short CFD      16/09/2004     Written         6,400              6.0308
Short CFD      17/09/2004     Written         8,331              6.1092
Short CFD      17/09/2004     Written         1,100              6.1207
Long CFD       20/09/2004     Written         133,500            6.0600
Short CFD      20/09/2004     Written         900                6.0757
Short CFD      20/09/2004     Written         1,200              6.0700
Short CFD      21/09/2004     Written         3,890              6.0700
Short CFD      23/09/2004     Written         13,500             5.8754
Long CFD       27/09/2004     Written         2,000              5.8450
Short CFD      27/09/2004     Entered into    14,492             5.8623
Short CFD      29/09/2004     Written         1,644              5.8250
Short CFD      30/09/2004     Written         7,051              5.7756
Short CFD      01/10/2004     Written         13,412             5.8150
Short CFD      01/10/2004     Written         3,075              5.8095
Short CFD      04/10/2004     Written         7,173              5.9928
Short CFD      04/10/2004     Written         16,274             5.9873
Short CFD      05/10/2004     Written         14,647             5.9391
Short CFD      05/10/2004     Written         5,017              5.9645
Long CFD       05/10/2004     Entered into    18,232             5.9582
Long CFD       06/10/2004     Written         16,704             5.8978
Short CFD      06/10/2004     Written         6,307              5.9000
Short CFD      06/10/2004     Written         5,000              5.9100
Short CFD      07/10/2004     Written         18,300             6.0164
Short CFD      08/10/2004     Written         15,690             5.9978
Short CFD      11/10/2004     Written         9,200              5.8450
Short CFD      11/10/2004     Entered into    50,155             5.8542
Long CFD       12/10/2004     Written         23,977             5.8109
Long CFD       13/10/2004     Written         5,700              5.8200
Short CFD      13/10/2004     Entered into    8,216              5.8000
Long CFD       14/10/2004     Written         52,826             5.1792
Long CFD       15/10/2004     Written         1,500              4.9850
Short CFD      15/10/2004     Written         1,988              5.1223
Short CFD      15/10/2004     Entered into    15,677             5.1500
Short CFD      15/10/2004     Entered into    137,517            5.1500
Short CFD      18/10/2004     Written         7,124              5.0700
Short CFD      19/10/2004     Written         4,500              5.1900
Short CFD      20/10/2004     Written         7,700              5.1127
Long CFD       21/10/2004     Written         6,015              5.2350
Short CFD      21/10/2004     Written         6,893              5.2500
Long CFD       25/10/2004     Written         16,882             5.1279
Short CFD