I put "Non Resident Tax Status" in Google and came up with this link.
http://www.hmrc.gov.uk/cnr/faqs_general.htm
A quick scan read I have COPY & Pasted these 2
Q3. In what circumstances would I become non-resident?
A3. Normally if you leave the UK to work abroad full-time, you will become not resident and not ordinarily resident in the UK if:
•your absence and employment from the UK covers a complete tax year (that is 6 April to 5 April)
•you spend less than 183 days in the UK during the tax year
•your visits to the UK do not average 91 days or more a tax year over a maximum of four years
From 6 April 2008, days when you are in the UK at the end of the day, that is midnight, are normally counted as days spent in the UK
Q13: In what circumstances will I be treated as a UK resident for UK tax purposes?
A13: To be treated as resident in the UK you must normally be physically present in the country at some time in the tax year. You will always be treated as resident if you are here for 183 days or more in the tax year. There are no exceptions to this. You count the total number of days you spend in the UK - it does not matter if you come and go several times during the year or if you are here for one stay of 183 days or more. If you are here for less than 183 days, you may still be treated as resident for the year if you visit the UK regularly and your visits average 91 days or more a tax year over a period not exceeding four years.
From 6 April 2008, days when you are in the UK at the end of the day, that is midnight, are normally counted as days spent in the UK.
END
The other thing is to check up on your NIC as you cant pay Class 1 while abroad. I think I paid Class 3 voluntary. Its all to do with your pension entitlement. The older you are the easier it is to find out if you have enough qualifiying years. You may have enough years already and decide not to pay any. You need to check.
If this is a short term contract, eg you go next month and its probably only 10months work you are probably too many days in the UK already for this tax year.
On edit. There are generally 365 days in a year. Leap years mess it up a bit