Are you resident in the UK for tax purposes?

Meaning of 'resident', 'ordinarily resident' and 'domiciled'
Resident
•if you're in the UK for 183 days or more in a tax year, you're a 'resident' for that year for tax purposes
•if you come to live in the UK permanently or to remain for three years or more you're resident from the date of arrival
•you're also treated as resident if you're in the UK for an average of 91 days or more in a tax year (worked out over a maximum of four consecutive tax years)
Ordinarily resident
•if you're resident in the UK year after year you will normally be treated as 'ordinarily resident'
•you're treated as ordinarily resident in the UK from the date you arrive if it's clear that you intend to stay for at least three years
Domiciled
•your domicile is normally acquired at birth, but this is a general law concept covering a range of factors
More than one of these definitions can apply to you - or even none of them at all.

If you're not resident in the UK for tax purposes you won't pay UK tax for work done overseas (but it may be taxable in another country).

source: http://www.direct.gov.uk/en/MoneyTaxAndBenefits/Taxes/LeavingOrComingIntoTheUK/DG_10026136