I currently have a request in with HMRC to clarify my situation, as I was in the same position last year.
First, you need to check the dual taxation situation between UK and your home country. That advice is here.
http://www.hmrc.gov.uk/international/dta-intro.htm Next, Haughtney1's reference is the latest info. It is quite straightforward as they now provide a flow diagram. If you can't follow it, then I suggest you need professional advice.
The big question, as others have said, is whether they will stand by the advice. In my case, as long as I have a letter from them confirming my tax status, I'm sorted, as I will not be working in UK again.
Reply due in a few weeks - I'll let you know what they say.