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 04/17/2003

                         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 POSTS LARGEST MARKET SHARE GAIN IN EUROPEAN OPTICAL NETWORKS MARKET IN
                                 2002 - REPORT



London, April 17, 2003 - A new report by the telecommunications research house
RHK states that Marconi (MONI) grew its market share in the European optical
networks market by four percentage points in 2002, the largest market share rise
of any equipment vendor during the period. RHK says in its report that Marconi
held a market leading position, alongside Alcatel, as a result. Marconi was also
identified as the clear leader in aggregation (synchronous digital hierarchy
multiplexing), being number one in traditional SDH aggregation and number two in
next-generation OED (optical edge devices).

In its market report entitled: "Alcatel and Marconi Top of Optical Class in
Europe", RHK found that both Marconi and Alcatel were top of the optical
networks leader board for Europe in 2002 with 21 per cent market share each.

Despite challenging market conditions, Marconi posted a four per cent market
share gain within the European optical networks market during 2002. RHK put
Marconi's success down, in part, to the company capitalising on the
infrastructure investment plans of its key customers in Europe, notably BT and
Telecom Italia.

The report also indicates that Marconi gained eight per cent of the European
market in aggregation - both traditional add-drop multiplexers and next
generation, where it now ranks first with 28 per cent of the market.

RHK defines European optical networking as the market for optical transport
equipment sold to network operators for their public or private (i.e. managed)
networks. According to RHK, Europe represented 26 per cent of the global market
in 2002, compared with 28 per cent in 2001. North America accounted for 30 per
cent and Asia-Pacific also represented 30 per cent, an increase of 12 per cent
from 2001.

"Our analysis shows that Marconi was able to strengthen its position, even
during difficult business conditions in the European optical networks industry,"
said Mark Lum, programme director for RHK's Optical Networks Europe practice.

"We are clearly pleased with RHK's findings, which gives us confidence in our
optical networks strategy, products and service. Particularly gratifying for
Marconi is the number two position gained in next-generation optical edge
devices, following the roll-out of Marconi's next-generation SDH portfolio,
launched in September 2002," said Martin Harriman, Marconi's chief marketing
officer.

ENDS/...

About Marconi plc

Marconi plc is a global telecommunications equipment and solutions company
headquartered in London. 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 aim is to help fixed
and mobile telecommunications operators worldwide reduce costs and increase
revenues.

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
http://www.marconi.com.

About RHK Inc

RHK is a research and advisory services firm assisting the world's leading
telecommunications companies. For more information visit http://www.rhk.com.

This press release contains forward-looking statements with respect to products,
partners, customers, future growth and other matters. Please refer to the Form
20-F report and Form 6-K reports filed by Marconi plc with the United States
Securities and Exchange Commission for a discussion of risks that could cause
actual results to differ materially from such statements.

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

Contacts

Joe Kelly

Public Relations

Marconi plc

+44 (0) 207 306 1771

+44 (0) 7801 722 931

joe.kelly@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: 04/17/2003