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  SUPPLEMENTAL AGREEMENT TO A SALE AND PURCHASE AGREEMENT DATED 16TH JUNE 1998
   ENTERED INTO BETWEEN INTER ALIA VISION NETWORKS III BV, COMTEL UK FINANCE
     B.V. AND NTL GROUP LIMITED IN RESPECT OF THE SALE AND PURCHASE OF THE
                            VISION NETWORKS UK GROUP

This Supplemental Agreement is made on the 22nd day of September 1998 by and
between:-

(1) VISION NETWORKS III B.V., a private limited liability company incorporated
in accordance with the laws of the Netherlands and having its registered office
at Hoofddorp and its principal place of business at Polarisavenue 41,2132 JH
Hoofddorp the Netherlands, for the purposes hereof duly represented by W.C.M.
van der Hoeven (hereinafter referred to as the "Seller");

(2) COMTEL UK FINANCE B.V. a private limited liability company incorporated in
accordance with the laws of the Netherlands and having its registered office at
Hoofddorp and its principal place of business at Polarisavenue 41,2132 JH
Hoofddorp the Netherlands for the purposes hereof duly represented by W.C.M. van
der Hoeven (hereinafter referred to as "ComTel");

(3) VISION NETWORKS (UK) I LIMITED, a private limited liability company
incorporated in England and having its registered office at Wharfedale Road,
Winnersh, Wokingham, Berkshire RG41 5TZ (hereinafter referred to as "UKI");

(4) TELECENTIAL COMMUNICATIONS (CANADA) LTD, a private limited liability company
incorporated in the Province of New Brunswick, Canada and having its registered
office at 300 Consilium Pl., Suite 1300, Scarborough, Ont. M1H 3G2 (hereinafter
referred to as "Canco 1");

(5) VISION NETWORKS (UK) II LIMITED, a private limited liability company
incorporated in England and having its registered office at Wharfedale Road,
Winnersh, Wokingham, Berkshire, RG41 5TZ (hereinafter referred to as "UKII");

(6) TELECENTIAL COMMUNICATIONS (UK) LIMITED, a private limited liability company
incorporated in the Province of New Brunswick, Canada and having its registered
office at 300 Consilium Pl., Suite 1300, Scarborough, Ont. M1H 3G2 aforesaid
(hereinafter referred to as "Canco 3");

(7) VISION NETWORKS UK HOLDING B.V. (IN LIQUIDATION) a private limited liability
company incorporated in accordance with the laws of the Netherlands and having
its registered office at Hoofddorp and its principal place of business at
Polarisavenue 41,2132 JH Hoofddorp the Netherlands for the purposes hereof duly
represented by its liquidator ComTel U.K. Finance B.V., represented by W.C.M.
van der Hoeven (hereinafter referred to as "VNUK")

(ComTel, UKI, Canco 1, UKII, Canco 3 and VNUK being hereafter referred to
jointly as the "Transferors" and individually as a "Transferor");

(8) VISION NETWORKS HOLDINGS B.V. a private limited liability company
incorporated in accordance with the laws of the Netherlands and having its
registered office at Hoofddorp and its principal place of business at
Polarisavenue 41,2132 JH Hoofddorp the Netherlands, for the purposes hereof duly
represented by W.C.M. van der Hoeven;
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(9) NTL GROUP LIMITED, a private limited liability company incorporated in
England and having its registered office at Bristol House, 1 Lakeside Road,
Farnborough, Hampshire, England (hereinafter referred to as the "Purchaser");

(10) NTL INC, a company incorporated and existing in accordance with the laws of
the State of Delaware, USA and having its principal place of business at 110
East 59th Street, 26th Floor, NYC 10022, USA (hereinafter referred to as the
"NTL");

(11) CABLETEL INVESTMENTS LIMITED, a private limited liability company
incorporated in England and having its registered office at Bristol House, 1
Lakeside Road, Farnborough, Hampshire, England (hereinafter referred to as
"CableTel Investments Limited");

(12) CABLETEL LIMITED, a private limited liability company incorporated in
England and having its registered office at Bristol House, 1 Lakeside Road,
Farnborough, Hampshire, England (hereinafter referred to as "CableTel Limited");
and

(13) NTL LIMITED, a private limited liability company incorporated in England
and having its registered office at Bristol House, 1 Lakeside Road, Farnborough,
Hampshire, England (hereinafter referred to as "NTL Limited").

WHEREAS

A.    The Seller, the Transferors, the Purchaser and NTL entered into a Sale and
      Purchase Agreement dated 16th June 1998 ("the Agreement");

B.    The parties to the Agreement wish to make certain amendments to the
      Agreement.

IT IS HEREBY AGREED AS FOLLOWS:-

1.    Articles 2 and 5.3 of the Agreement provide for the sale and assignment of
      various Partnership Interests to the Purchaser or its nominee. The
      Purchaser hereby nominates CableTel Investments Limited, CableTel Limited
      and NTL Limited for the purposes of Articles 2 and 5.3 of the Agreement to
      the extent set out in and in accordance with the following provisions of
      this Article. Accordingly, Articles 2 and 5.3 of the Agreement shall be
      varied so that:-

      1.1   UK I shall sell and assign absolutely its Partnership Interest as a
            general partner in the Telecential Communications Partnership to
            CableTel Investments Limited which Canco 1 and UK I shall procure
            becomes a general partner of the Telecential Communications
            Partnership ("P1") (and by virtue thereof a general partner of the
            Telecential Communications (Herts) Partnership ("P3") and the
            Telecential Communications (Northants) Partnership) ("P4") in place
            of UK I;

      1.2   UK II shall assign absolutely all its Partnership Interest as a
            limited partner in LP5 to NTL Limited and Canco 3 and UK II shall
            procure that NTL Limited becomes a limited partner of LP5 in place
            of UK II;

      1.3   VNUK shall assign absolutely all its Partnership Interest as a
            limited partner in LP6 to NTL Limited and Canco 3 and VNUK shall
            procure that NTL Limited becomes a limited partner of LP6 in place
            of VNUK;


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      1.4   Canco 1 shall sell and assign absolutely all its Partnership
            Interest as managing general partner in P1 to CableTel Limited and
            Canco 1 and UK I shall procure that CableTel Limited becomes
            managing general partner of P1 (and by virtue thereof, a general
            partner of P3 and P4) in place of Canco 1; and

      1.5   Canco 3 shall sell and assign absolutely all its Partnership
            Interest as managing general partner in LP5 and LP6 to CableTel
            Limited and Canco 3 and UK II and Canco 3 and VNUK respectively
            shall procure that CableTel Limited becomes managing general partner
            of LP5 and LP6 respectively in place of Canco 3.

      and for the purposes of effecting the same, Canco 1, Canco 3, UK I, UK II,
      VNUK, CableTel Limited, CableTel Investments Limited and NTL Limited shall
      enter into Deeds of Retirement and Appointment in the forms contained in
      Schedules O, P and Q to the Agreement.

      The Partnership Interests to be sold and/or assigned to CableTel
      Investments Limited, NTL Limited and CableTel Limited (as the case may be)
      shall be sold to CableTel Investments Limited, CableTel Limited and/or NTL
      Limited absolutely in their own right and not on behalf of the Purchaser.

2.    Article 7 of the Agreement and Schedule R thereto shall be varied:-

      2.1   so that, subject as provided in those provisions of Article 7 not
            hereby varied, the representations and warranties in respect of the
            Telecential Group given by the Seller and the Transferors shall be
            given to each of the Purchaser, CableTel Investments Limited, NTL
            Limited and CableTel Limited except that no such warranties and
            representations shall be given in respect of the Further
            Subsidiaries (as defined in clause 12 below) or:-

            2.1.1 to CableTel Investments Limited in respect of LP5, LP6,
                  Heartland Cablevision (UK) Limited, Heartland Cablevision II
                  (UK) Limited, ComTel Limited, Maza Limited, Herts Cable
                  Limited and Northampton Cable Television Limited;

            2.1.2 to the Purchaser in respect of the Telecential Group other
                  than ComTel Limited, Maza Limited, Herts Cable Limited and
                  Northampton Cable Television Limited;

            2.1.3 to NTL Limited in respect of the Telecential Group other than
                  LP5, LP6, Heartland Cablevision (UK) Limited and Heartland
                  Cablevision II (UK) Limited; or

            2.1.4 to CableTel Limited in respect of ComTel Limited, Maza
                  Limited, Herts Cable Limited and Northampton Cable Television
                  Limited; and

      2.2   so that any claim arising out of a breach of such representations
            and warranties given by the Seller and the Transferors may be
            brought by each of the Purchaser, NTL Limited, CableTel Limited and
            CableTel Investments Limited (as applicable),


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      Provided that for the avoidance of doubt, references in Article 9 to the
      Purchaser shall be deemed to refer also to NTL Limited, CableTel Limited
      and/or CableTel Investments Limited (as the case may be) in respect of any
      such claim as may be brought by any of them in respect of any Breach or
      Non-fulfilment.

3.    Article 12.15 of the Agreement shall be varied so that references to the
      Purchaser shall also refer to each of CableTel Investments Limited,
      CableTel Limited and NTL Limited and references in such Article to the
      "Agreement" shall include the Deeds of Retirement and Appointment referred
      to in clause 1 above.

4.    Article 6.4 of the Agreement shall be varied so that the number and words
      "80 (in words : eighty)" shall be inserted in substitution for the number
      and words "70 (in words : seventy)" where they appear in the second line
      of Article 6.4 of the Agreement and the number and words "90 (in words :
      ninety)" shall be inserted in substitution for the number and words "80
      (in words : eighty)" where they appear in the fourth line of Article 6.4
      of the Agreement.

5.1   Article 4.3 of the Agreement shall be varied so that completion of the
      sale and purchase of the Telecential Assets will take place at the offices
      of Allen & Overy in London, UK on 22 September 1998 (which,
      notwithstanding any other provision of the Agreement, shall for the
      purposes of the Agreement be the "Telecential Completion Date") when the
      transfer of the Telecential Assets will take place in accordance with
      Article 5.3 of the Agreement except that the deeds of retirement and
      appointment referred to in Articles 5.3.2, 5.3.3 and 5.3.4 of the
      Agreement shall be signed by Canco 1, UK I, Canco 3, UK II and VNUK in the
      Netherlands and delivered to the offices of Travers Smith Braithwaite,
      Douglas, Isle of Man on such date and the counterparts of such deeds of
      retirement and appointment shall be signed by CableTel Investments
      Limited, CableTel Limited and NTL Limited at Douglas, Isle of Man and
      delivered to the offices of Loeff Claeys Verbeke, Amsterdam, the
      Netherlands on behalf of the Seller and the Transferors on such date.

5.2   Article 5.3.1(b) shall be amended by the inclusion of the words ",
      Pirunico Nominees (Jersey) Limited or Praetor Trust Company Limited" after
      the words "other than those appointed by Pirunico Trustees (Jersey)
      Limited".

5.3   Article 5.3.6 of the Agreement shall be varied so that:-

      5.3.1 the Seller's obligations in respect of the passing of Board
            Resolutions of HCL and NCTL (as defined in Article 15 of the
            Agreement) shall be to use its reasonable endeavours, subject to the
            provisions of the Minority Interest Agreements (as similarly
            defined), to procure the passing of such Resolutions; provided that
            the Seller shall in any event procure the appointment of the
            Purchaser's nominees as directors of HCL and NCTL as "A" directors
            in accordance with the Articles of Association of HCL and NCTL,
            respectively, subject only to compliance by the Purchaser's nominees
            with their obligations in respect of such appointment under the
            Minority Agreements; and

      5.3.2 the Seller's obligations in respect of the passing of Board
            Resolutions of Chiltern Cable Limited shall be to procure the
            appointment of the 


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            Purchaser's nominees as "A" directors in accordance with the
            Articles of Association of Chiltern Cable Limited.

6.    Article 6.8 of the Agreement shall be amended such that:-

      6.1   the total amount of cash and equivalents in hand or at a bank as
            shown in the Completion Balance Sheet shall be an increase to the
            cash element of the Purchase Price and the sum of pound sterling
            9,558,000 in respect of which amount shall be paid by the Purchaser
            to the Seller on the Telecential Completion Date, PROVIDED that in
            the event that the total amount of cash and equivalents in hand or
            at a bank as shown in the Completion Balance Sheet is not pound
            sterling9,558,000, the Purchaser shall pay any excess over pound
            sterling9,558,000 to the Seller or the Seller shall pay any
            shortfall under pound sterling9,558,000 to the Purchaser (as the
            case may be) not later than the fifth business day after agreement
            or determination of the Completion Balance Sheet in accordance with
            Article 6 of the Agreement; and

      6.2   there shall be deducted from the Purchase Price to be paid by the
            Purchaser on the Telecential Completion Date the cost (net of any
            associated credit note) of the acquisition of any relevant asset to
            the Purchaser or any subsidiary of the Purchaser in the event that
            the Purchaser or such subsidiary acquires such asset from a third
            party which is a lessor of such asset to a ComTel Company or member
            of the Telecential Group in connection with the prepayment or
            termination of any financial lease which constituted Indebtedness
            (which deduction it is agreed shall amount to pound
            sterling73,888.24 in total),

      the balance of the amount referred to in clause 6.1 above remaining after
      deduction of the amount referred to in clause 6.2 above being referred to
      in the Agreement as the "Cash Adjustment".

7.    In Schedule D to the Agreement, the definition of "Indebtedness" shall be
      varied so as to exclude any liabilities owed by any ComTel Company to any
      other ComTel Company and any liabilities owed by any member of the
      Telecential Group to any other member of the Telecential Group.

8.    Without prejudice to accrued rights under those Articles, the Seller and
      the Transferors covenant as at the date hereof to the Purchaser, CableTel
      Investments Limited, CableTel Limited and NTL Limited in the same terms,
      mutatis mutandis, as Articles 3.2 and 3.4 of the Agreement, the Purchaser
      covenants as at the date hereof to ComTel in the same terms, mutatis
      mutandis, as clause 4.7 of the Relationship Agreement dated 16 June 1998
      between ComTel, the Purchaser and the ComTel Companies (as defined in that
      agreement) and the Seller, the Transferors, the Purchaser, CableTel
      Investments Limited, CableTel Limited and NTL Limited covenant as at the
      date hereof with each other mutatis mutandis in accordance with Article 10
      of the Agreement.

9.    Vision Networks Holdings BV hereby confirms the terms of its guarantee
      dated 26 August 1998 in favour of NTL Group Limited notwithstanding the
      terms of this Supplemental Agreement and confirms that the benefit of such
      guarantee shall extend to CableTel Investments Limited, CableTel Limited
      and NTL Limited (in addition to the Purchaser) in respect of the
      obligations of the Seller and the 


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      Transferors to any of them under the Agreement as amended by this
      Supplemental Agreement.

10.   Part 2 of Schedule Ind to the Agreement shall be deleted and Schedule 1
      annexed to this Supplemental Agreement shall be inserted in substitution
      therefor.

11.   The Purchaser and ComTel agree that paragraph 2 of Part 1 of Schedule 1 to
      the Relationship Agreement dated 16 June 1998 between ComTel, the
      Purchaser and the ComTel Companies (as defined in that agreement) shall be
      amended by the insertion of the following words at the end of that
      paragraph:-

      "Provided that so long as Telecential Completion takes place on 22nd
      September 1998,

      (a)   NTL's obligations to pay such fee shall be only to pay such fee to
            the extent that in the aggregate this exceeds pound sterling 3.5
            million (the "Excess Amount"). Any Excess Amount payable by NTL
            shall be paid simultaneously with payment of the Purchase Price (as
            defined in the Principal Agreement) on the Telecential Completion
            Date; and

      (b)   the Excess Amount shall be pound sterling 427,553.00"

12.   The Seller, ComTel and the Purchaser acknowledge that although not
      included in Schedule Z of the Agreement, ComTel Limited, a member of the
      Telecential Group, has two further subsidiary companies namely South
      Yorkshire Cablevision (UK) Limited and Chiltern Cable Limited (together
      the "Further Subsidiaries"). The existence of the Further Subsidiaries
      shall not be treated as a breach of the Warranties given by the Seller and
      the Transferors. The Seller and ComTel represent and warrant to the
      Purchaser :-

12.1  ComTel Limited is the legal and a member of the Telecential Group is the
      beneficial owner of the entire issued share capital of South Yorkshire
      Cablevision (UK) Limited which shares are validly issued and fully paid
      up;

12.2  ComTel Limited is the legal and a member of the Telecential Group is the
      beneficial owner of 160 A Ordinary Shares of pound sterling 1 each in the
      capital of Chiltern Cable Limited, which shares carry the right to
      exercise 80% of the votes which may be cast at general meetings of that
      company, subject to the rights of the holder of the C Special Rights
      Redeemable Shares in the capital of the company as set out in the Articles
      of Association of the Company, and are validly issued and fully paid up;

12.3  no person has any right to call for the transfer of any shares of South
      Yorkshire Cablevision (UK) Limited or any A Ordinary Shares of pound
      sterling 1 each in the capital of Chiltern Cable Limited in each case held
      by ComTel Limited or, so far as the Seller and ComTel are aware, no person
      has the right to call for the issue of any such shares except in each case
      as set out in the Articles of Association of such Further Subsidiary and
      none of the shares in these companies held by ComTel Limited are subject
      to any liens or charges of any kind or any encumbrances or interests in
      favour of any other person;


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12.4  neither South Yorkshire Cablevision (UK) Limited nor Chiltern Cable
      Limited have any liabilities or have ever traded and both are dormant
      companies within the meaning of the Companies Acts 1985 (as amended).

      The Seller and ComTel hereby covenant to indemnify and keep indemnified
      South Yorkshire Cablevision (UK) Limited, Chiltern Cable Limited and the
      Purchaser (for itself and as trustee for South Yorkshire Cablevision (UK)
      Limited and Chiltern Cable Limited) against all liabilities, costs and
      expenses (including Tax and any liability to Tax) and all actions incurred
      by any of them as a result of or arising out of or in connection with any
      liabilities which South Yorkshire Cablevision (UK) Limited and Chiltern
      Cable Limited may have as at or incurred prior to Telecential Completion.
      The Seller and ComTel further hereby covenant to indemnify and keep
      indemnified the Purchaser for itself and as trustee for each member of the
      Telecential Group against all liabilities, costs and expenses incurred by
      any of them in respect of or arising out of or in connection with any
      obligation of them to provide funding (whether in the form of debt or
      equity subscription) to either of the Further Subsidiaries which
      obligation is in force (either as an actual or contingent obligation) as
      at the date of this Supplemental Agreement. The Seller and ComTel shall
      cease to have any liability under this clause 12 (save for any liability
      already accrued due thereunder or notified in writing prior thereto) on
      and following the tenth anniversary of the Telecential Completion Date.
      Neither the Seller nor ComTel shall be liable in respect of any losses or
      liabilities arising in connection with either or both of the Further
      Subsidiaries except to the extent of their obligations under clauses 5 and
      12 of this Supplemental Agreement. For the avoidance of doubt, the Seller
      and ComTel shall have no liability under this clause 12 in respect of any
      obligations of the Further Subsidiaries or any obligation of any of the
      parties listed in (10) through (13) above not accrued or existing, or in
      respect of any liabilities or losses suffered by any such parties in
      connection with any actions taken by either of the Further Subsidiaries
      except pursuant to obligations accrued or existing, (and in each case
      whether actual or contingent) at the date of this Agreement. None of the
      provisions of Articles 7, 9 and 11 of the Agreement shall apply to this
      clause or the Further Subsidiaries. References in the Agreement to members
      of the Telecential Group shall include South Yorkshire Cablevision (UK)
      Limited and Chiltern Cable Limited.

13.1  Subject as more particularly mentioned in clause 13.3 below, the cash
      element of the Purchase Price shall be increased by pound sterling250,000
      which sum shall be payable by the Purchaser to the Seller at Telecential
      Completion.

13.2  For the avoidance of doubt, payments in the ordinary course by any member
      of the Telecential Group in accordance with the terms of any Indebtedness
      (other than any prepayment or termination charges and associated costs)
      shall be for the account of the relevant member of the Telecential Group
      and shall not be treated as forming part of Indebtedness and their
      discharge shall not be treated as being for the account of the Seller or
      any Transferor.


13.3  The Parties acknowledge that the cash element of the Purchase Price
      payable by the Purchaser on the Telecential Completion Date in accordance
      with the terms of the Agreement (as amended hereby) shall be the "Total
      Receivable" amount set out in Schedule 2 annexed hereto.


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13.4  The Seller hereby agrees that in the event that Telecential Completion
      occurs on 22 September 1998, the Seller shall not be entitled to any
      interest on the loan referred to in Article 3.3 of Agreement.

14.1  Article 12 (other than Articles 12.1 to 12.3 (inclusive), 12.13A, 12.14,
      12.15 (but without prejudice to the effect of clause 3 hereof), 12.16,
      12.19, 12.20 and 12.21) shall be incorporated in this Supplemental
      Agreement as if set out in full herein by reference to this Supplemental
      Agreement. For the purposes of Article 12.4 of the Agreement as so
      incorporated, the address and telefax details for notices or other
      communications to be given to Vision Networks Holdings BV shall be the
      same as those for the Seller and Transferors.

14.2  Except as expressly set out herein, capitalised terms defined in the
      Agreement shall have the same meaning in this Supplemental Agreement.

14.3  References in the Agreement to the "Agreement" shall be deemed to refer to
      the Agreement as varied by this Supplemental Agreement and references in
      the Agreement to the "Parties" shall include NTL Limited, CableTel
      Limited, CableTel Investments Limited and Vision Networks Holdings B.V..

15.   Except to the extent varied hereby, the parties confirm the terms of the
      Agreement.

AS WITNESS this Supplemental Agreement has been executed by the parties hereto
on the date first above written.


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                                   SCHEDULE 1

                                  INDEBTEDNESS


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                                   SCHEDULE 2

                                 PURCHASE PRICE


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SIGNED on behalf of                  )
VISION NETWORKS III B.V.                     )
acting by                                    )       W.C.M. van der Hoeven
its director/duly authorised officer )





SIGNED on behalf of                  )
COMTEL UK FINANCE B.V.                       )
acting by                                    )       W.C.M. van der Hoeven
its director/duly authorised officer )





SIGNED on behalf of                  )
VISION NETWORKS (UK) I LIMITED       )
acting by                                    )       D.D. Adams
its director/duly authorised officer )





SIGNED on behalf of                  )
TELECENTIAL COMMUNICATIONS           )
(CANADA) LIMITED                     )
acting by                                    )       D.D. Adams
its director/duly authorised officer )





SIGNED on behalf of                  )
VISION NETWORKS (UK) II LIMITED      )
acting by                                    )       D.D. Adams
its director/duly authorised officer )





SIGNED on behalf of                  )
VISION NETWORKS HOLDINGS B.V.        )
acting by                                    )       W.C.M. van der Hoeven
its director/duly authorised officer )


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SIGNED on behalf of                  )
TELECENTIAL COMMUNICATIONS           )
(UK) LIMITED                                 )
acting by                                    )       D.D. Adams
its director/duly authorised officer )





SIGNED on behalf of                  )
VISION NETWORKS UK HOLDING           )
B.V. (IN LIQUIDATION)                        )
acting by                                    )       W.C.M. van der Hoeven
its director/duly authorised officer )





SIGNED on behalf of                  )
NTL GROUP LIMITED                    )
acting by                                    )       R.M. Mackenzie
its director/duly authorised officer )





SIGNED on behalf of                  )
NTL INC.                             )
acting by                                    )       J. Gregg
its director/duly authorised officer )





SIGNED on behalf of                  )
CABLETEL INVESTMENTS LIMITED         )
acting by                                    )       R.M. Mackenzie
its director/duly authorised officer )


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SIGNED on behalf of                  )
CABLETEL LIMITED                     )
acting by                                    )       R.M. Mackenzie
its director/duly authorised officer )





SIGNED on behalf of                  )
NTL LIMITED                                  )
acting by                                    )       R.M. Mackenzie
its director/duly authorised officer )


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