SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                    FORM 6-K


                            Report of Foreign Issuer

                      Pursuant to Rule 13a-16 or 15d-16 of
                       the Securities Exchange Act of 1934


                          For the Month of May 9, 2003

                         Commission file number: 0-30924


                                   MARCONI PLC

             (Exact name of Registrant as specified in its Charter)


                                   4th Floor
                                 Regents Place
                                338 Euston Road
                                    London
                                    NW1 3BT
                    (Address of principal executive offices)


(Indicate by check mark whether the registrant files or will file annual
reports under cover Form 20-F or Form 40-F.)


                             Form 20-F X   Form 40-F


(Indicate by check mark whether the registrant by furnishing the information
contained in this Form is also thereby furnishing the information to the
Commission pursuant to Rule 12g3-2(b) under the Securities Exchange
Act of 1934.)


                                   Yes   No X


              CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS


In order to utilize the "Safe Harbor"  provisions  of the United States  Private
Securities  Litigation Reform Act of 1995 (the "Reform Act"),  Marconi plc ( the
"Company")  is  providing  the  following  cautionary   statement.   Except  for
historical information contained herein,  statements contained in this Report on
Form 6-K may constitute  "forward-looking  statements" within the meaning of the
Reform Act. The words "believe",  "anticipate",  "expect", "intend", "estimate",
"plan",  "assume",  "positioned",   "will",  "may",  "risk"  and  other  similar
expressions which are predictions of or indicate future events and future trends
which do not relate to historical matters identify  forward-looking  statements.
Reliance should not be placed on such statements  because they involve known and
unknown  risks,  uncertainties  and other factors which are in some cases beyond
the control of the Company,  together with its subsidiaries  (the "Group"),  and
may cause the actual results, performance or achievements of the Group to differ
materially  from  anticipated   future  results,   performance  or  achievements
expressed or implied by such forward-looking  statements (and from past results,
performance or  achievement).  Certain  factors that may cause such  differences
include  but are not  limited  to the  following:  (1) any major  disruption  in
production  at our key  facilities;  (2) changes in the  environmental,  tax and
other laws and regulations,  which, among other things,  could cause us to incur
substantial additional capital expenditures and operation and maintenance costs;
and (3) adverse  changes in the markets for our products,  including as a result
of increased  competition in the highly  competitive  international  markets for
such products. These and other risks, uncertainties and factors are discussed in
the  Company's  Registration  Statement  on Form F-1 and other  filings with the
Securities and Exchange  Commission,  including this Form 6-K.  Shareholders and
prospective  investors  are  cautioned  not to  place  undue  reliance  on these
forward-looking  statements which speak only as to the Company's  judgment as of
the date hereof.  Any such  forward-looking  statements are not intended to give
any  assurance as to future  results.  The Company  undertakes  no obligation to
publicly update or revise any of these  forward-looking  statements,  whether to
reflect new information or future events or circumstances or otherwise.


                                  Marconi plc

      Amendment to Historic Sales Information contained in Trading Update

London - 9 May 2003 - Marconi  (MONI) today  provided a correction to Appendix 2
of its Trading  Update  dated 7 May 2003 in relation to the  historic  quarterly
breakdown of sales by product area for the year ended 31 March 2002.

The table below sets forth the corrected information.

Core Sales by Product Area for the year ended 31 March 2002




in GBP million                                                  FY02
                                                        Q1     Q2     Q3     Q4
                                                                

  Optical Networks                                     146    211    189    191
  Broadband Routing and Switching (BBRS)                52     61     40     56
  European Access                                       78    111     85     87
  North American Access                                 34     31     24     32
  Outside Plant & Power (OPP)                           91     65     48     43
  Other Network Equipment                               25     38     21     45
  Network Equipment                                    426    517    407    454
  Installation, Commissioning & Maintenance (IC&M)     126    145    122    135
  Value-Added Services (VAS)                            98    136    103    104
  Network Services                                     224    281    225    239
  Core                                                 650    798    632    693




Ends

Notes to Editors

About Marconi plc

Marconi plc is a global telecommunications  equipment and solutions company. The
company's  core  business is the provision of  innovative  and reliable  optical
networks,  broadband routing and switching and broadband access technologies and
services.  The company's  customer  base  includes  many of the world's  largest
telecommunications operators.

The  company  is listed on the London  Stock  Exchange  under the  symbol  MONI.
Additional information about Marconi can be found at www.marconi.com.

Copyright (c) 2003 Marconi plc. All rights reserved. All brands or product names
are trademarks of their respective holders.

Contacts

Name:       David Beck / Joe Kelly           Heather Green

Title:      Public Relations                 Investor Relations

Phone:      +44 (0) 207 306 1771             +44 (0) 207 306 1735

            +44 (0) 207 306 1490

            joe.kelly@marconi.com             heather.green@marconi.com



                                   SIGNATURES

Pursuant  to the  requirements  of the  Securities  Exchange  Act of  1934,  the
registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned, thereunto duly authorized.


                                       MARCONI PLC



                                       By:     ____M Skelly____

                                       Name:   M Skelly
                                       Title:  Company Secretary


Date: 9 May 2003