FORM 6-K

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                        Report of Foreign Private Issuer


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


                                 26 January 2005


                                    mmO2 plc


                                Wellington Street
                       Slough, Berkshire SL1 1YP, England

                    (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...


If "Yes" is marked, indicate below the file number assigned to the registrant
in connection with Rule 12g3-2(b): 82 ________


Enclosure:

Copy of announcement regarding Holding(s) in Company sent to the
London Stock Exchange on 26 January 2005



                                SCHEDULE 10

                 NOTIFICATION OF MAJOR INTERESTS IN SHARES

1. Name of company

mmO2 plc


2. Name of shareholder having a major interest

The Capital Group Companies, Inc.


3. Please state whether notification indicates that it is in respect of holding
of the shareholder named in 2 above or in respect of a non-beneficial interest
or in the case of an individual holder if it is a holding of that person's
spouse or children under the age of 18

In respect of 2 above


4. Name of the registered holder(s) and, if more than one holder, the number of
shares held by each of them



Capital Guardian Trust Company

Registered Name                                  Number of Shares
                                              
Chase Nominees Limited                           2,625,200
Woolgate House
Coleman Street
London EC2P 2HD

Nortrust Nominees                                1,999,500
155 Bishopsgate
London EC2M 3XS

Mellon Nominees (UK) Limited                     210,700
150 Buchanan Street
Glasgow G1 2DY


Capital International Limited

State Street Nominees Limited                     2,373,560
Canary Wharf
27th Floor, 1 Canada Square
London E14 5AF

Bank of New York Nominees                         47,489,460
Bank of New York
3 Birchin Lane
London
EC3V 9BY

Northern Trust                                    13,442,121
c/o NorTrust Nominees Limited
155 Bishopsgate
London EC2M 3XS

Chase Nominees Ltd                                21,209,500
Woolgate House
Coleman Street
London EC2P 2HD

Midland Bank plc                                  1,372,200
5 Laurence
Poutney Hill
London EC4R OE

Bankers Trust                                     1,530,508
59 1/2 Southmark Street
2nd Floor
London SE1 OHH

Barclays Bank                                     1,182,100
Barclays Global Securities Services
8 Angel Court
London EC2R 7HT

Citibank London                                   3,035,369
11 Old Jewry
London EC2R 8D8

Morgan Guaranty                                   2,081,100
83 Pall Mall
London SW1Y 5ES

Nortrust Nominees                                 29,554,479
155 Bishopsgate
London EC2M 3XS

State Street Bank & Trust Co                      8,765,573

Citibank                                          777,669

Deutsche Bank AG                                  8,114,429
23 Great Winchester Street
London EC2P 2AX

HSBC Bank plc                                     6,896,189
Securities Services
Mariner House
Pepys Street
London EC3N 4DA

Mellon Bank N.A.                                  2,295,100
London Branch
London

Northern Trust AVFC                               1,663,614
South Africa
KAS UK 172,500
Kass Associate
PO Box 178
1000 AD Amsterdam

Mellon Nominees (UK) Ltd                          937,200
150 Buchanan Street
Glasgow G1 2DY

Bank One London                                   1,634,900

Clydesdale Bank plc                               96,200


Capital International S.A.:

Chase Nominees Limited                            4,177,877
Woolgate House
Coleman Street
London EC2P 2HD

Midland Bank plc                                  42,300
5 Laurence
Poutney Hill
EC4R OE

Royal Bank of Scotland                            161,500
Regents House
42 Islington High Street
London N1 8XL

State Street Bank & Trust Co.                     257,600

Lloyds Bank                                       152,800
Central Settlement Section
Branches Stock Office
34 Threadneedle Street
London

Citibank NA                                       94,000
Toronto

HSBC Bank plc                                     782,800
Securities Services
Mariner House
Pepys Street
Lndon EC3N 4DA


Capital International, Inc.:

State Street Nominees Limited                     8,471,913
Canary Wharf
27th floor, 1 Canada Square
London E14 5AF

Bank of New York Nominees                         2,449,629
Bank of New York
3 Birchin Lane
London EC3V 9BY

Northern Trust                                    199,100
c/o NorTrust Nominees Limited
155 Bishopsgate
London EC2M 3XS

Chase Nominees Limited                            10,684,524
Woolgate House
Coleman Street
London EC2P 2HD

Midland Bank plc                                  180,900
5 Laurence
Poutney Hill
London EC4R 0E

Bankers Trust                                     65,900
59 1/2 Southmark Street
2nd Floor
London SE1 0HH

Citibank London                                   134,300
11 Old Jewry
London EC2R 8DB

Nortrust Nominees                                 864,000
155 Bishopsgate
London EC2M 9XS

State Street Bank & Trust Co.                     2,344,194

Citibank                                          126,600

Citibank NA                                       1,569,806
Toronto

HSBC Bank plc                                     156,674
Securities Services
Mariner House
Pepys Street
London EC3N 4DA

JP Morgan Chase Bank                              393,400


Capital Research and Management Company:


State Street Nominees Limited                     272,719,322
Canary Wharf
27th Floor, 1 Canada Square
London E14 5AF

Chase Nominees Limited                            162,367,900
Woolgate House
Coleman Street
London
EC2P 2HD

State Street Bank & Trust Co.                     222,800


5. Number of shares / amount of stock acquired

18,353,459


6. Percentage of issued class

0.21%


7. Number of shares / amount of stock disposed

N/A


8. Percentage of issued class

N/A


9. Class of security

Ordinary shares of 0.1p each


10. Date of transaction

24 January 2005 - Date of Section 198 Notification


11. Date company informed

26 January 2005


12. Total holding following this notification

628,079,010


13. Total percentage holding of issued class following this notification

7.223%


14. Any additional information

Notification in respect of section 198 Companies Act 1985


15. Name of contact and telephone number for queries

Timothy Maw - 01753 628 293


16. Name and signature of authorised company official responsible for making
this notification

Timothy Maw


Date of notification

26 January 2005


The FSA does not give any express or implied warranty as to the accuracy of this
document or material and does not accept any liability for error or omission.
The FSA is not liable for any damages (including, without limitation, damages
for loss of business or loss of profits) arising in contract, tort or otherwise
from the use of or inability to use this document, or any material contained in
it, or from any action or decision taken as a result of using this document or
any such material.



                              SIGNATURE

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.



                                                 mmO2 plc


Date: 26 January 2005                By:___/s/ Robert Harwood___

                                           ROBERT HARWOOD
                                           Assistant Secretary