Exhibit 4.13 LLOYDS TSB CORPORATE City of London Lloyds TSB Bank plc PO Box 18436 39 Threadneedle Street London Telephone: 020 7670 3733 EC2R 8PT Facsimile: 020 7670 3769 Reference: MC The Directors Date: 16th January 2006 VTL (UK) Limited Incubon House Wick Road Egham TW20 0HR Dear Sirs, AMENDMENT LETTER We refer to a letter dated 21st October 2005 (the "Facility Letter") and to the security documents required to be effected thereby from time to time. Pursuant to the foregoing we agreed to make available to you a revolving loan of up to (pound)5,750,000 (the "Facility"). We hereby confirm that, provided the preconditions set out below have been satisfied prior to 31 January 2006 (the "Effective Date") the following amendments shall be made to the Facility Letter with effect from the Effective Date: 1. for all purposes the Facility Letter shall be read and construed as if the amount of the Facility therein provided were (pound)7,000,000 (seven million pounds sterling) and not (pound)5,750,000 (five million, seven hundred and fifty thousand pounds sterling) and all references to (pound)5,750,000 shall be deemed to be references to (pound)7,000,000, and 2. the definition of "Expiry Date" in clause 1 shall be amended to read: "Expiry Date means 30th April 2006". 3. the definition of "Facility Limit" in clause 1 shall be amended to read: "Facility Limit" means (pound)7,000,000 subject to any cancellation or other reduction thereof within the terms of this letter. From the Effective Date the Facility Letter and this letter shall be construed as one agreement and all references in the Facility Letter to "this letter", "herein", "hereof", and terms of similar effect shall, unless the context otherwise requires, be deemed to be references to the Facility Letter as amended by this letter. All other terms and conditions expressed in the Facility Letter remain unaltered. As a precondition to the above amendments becoming effective the Bank is to receive in a form and substance acceptable to the Bank: (a) a copy of this letter duly signed by you in acceptance of the amendments contained herein; (b) a certified copy of your board resolution approving the terms of this letter and authorising a person or persons to sign on your behalf the acknowledgement appearing on the duplicate copy of this letter; (c) if not already in our possession, duly authenticated specimen signatures of the person(s) so authorised; (d) such evidence as the Bank shall require to confirm that the principal amount of the guarantee detailed in Clause 4.2 of the Facility Letter has been increased to (pound)7,250,000; and (e) an arrangement fee of (pound)12,500. Yours faithfully, For and on behalf of Lloyds TSB Bank plc /s/ Mark Jones Mark Jones 2 Continuation of a letter from Lloyds TSB Bank plc to: VTL (UK) Limited Relationship Manager 3 Continuation of a letter from Lloyds TSB Bank plc to: VTL (UK) Limited We hereby acknowledge receipt of your letter dated 16th January 2006 of which this is a duplicate and confirm our agreement to the amendments therein contained, pursuant to a resolution of the board dated 20th January 2006. Please debit the arrangement fee to our current account number 2524060. For and on behalf of VTL (UK) Limited Signed by Lucy Woods (name) Stuart Blythe (name) /s/ Lucy Woods (signature) /s/ Stuart Blythe (signature) 20th January 2006 (date) 20th January 2006 (date) THIS LETTER CREATES LEGAL OBLIGATIONS. BEFORE SIGNING YOU MAY WISH TO TAKE INDEPENDENT ADVICE.