Tax when leaving the UK

When you leave the UK you need to work out whether there is any change to your tax affairs and notify HM Revenue & Customs (HMRC). You may need to complete a Self Assessment tax return and you might be able to claim some tax back.

You must tell HMRC if you're:

• leaving the UK to live or work abroad
• returning home or moving to another country after a period of living and working in the UK

If you're not required to fill in a tax return, you'll have to complete form P85 'Leaving the UK - getting your tax right' by following the link below. Please read the 'About this form' section on the form carefully before deciding whether or not you should complete it.
HMRC will use the information on the form to send you any tax refund you're owed and work out if you'll become non-resident. It's important you enclose parts 2 and 3 of form P45 if you have one as HMRC will not be able to make any tax refund you are owed without them. You'll need to send the original versions - photocopies won't be accepted.
If you're leaving the UK to work full-time abroad for a UK based employer for at least a complete tax year, you'll need to fill in a tax return as well as a form P85.
Please note that you cannot reclaim any National Insurance contributions you paid as part of your job in the UK.

source: http://www.hmrc.gov.uk/international/leave-uk.htm