It also depends on if you wish to claim split-year treatment to claim back UK tax paid on interest, etc. To claim split-year treatment you need to be resident in the UK for less than 183 days in the tax year. There are more details on this and FAQs on other non-resident tax matters here:
http://www.hmrc.gov.uk/cnr/faqs_general.htm#1nr
We have successfully claimed tax refunds under the split-year treatment both times we have returned to the UK after living overseas and when we left the UK for New Zealand, and we did it through our self-assessment tax returns.