As of 1 September:
Procedure for problems with Xbox 360 consoles (Local and UK imports) Updated for 1 September 2008
1) Call Microsoft SA on 0800991550 and they will troubleshoot the machine with you. If they find that the machine is indeed faulty and can be replaced as per the warranty conditions, then they will give you a reference number.
2) Once you have the reference number you can contact MI Digital directly to make the necessary arrangements to collect and/or replace the unit. The contact number is (011) 997-5000 and the contact persons are Cathy or Bernice. You will also need to have your proof of purchase (from Take2 or any other retailer) on hand as it will be requested.
Please download the PDF file below to get the complete instructions what to do with regards to your faulty Xbox 360 Console.
Source Take 2.
Check at the bottom of the page:
Take 2 - Help - Returns