The residence and presence conditions for UK contribution liability (and eligibility to make voluntary contributions) are as follows but may, of course, be overridden by EC Regulations or treaty rules.
Class 1 primary contributions
An employed earner is liable to primary Class 1 contributions if he is resident or present in the UK, disregarding any temporary absence (such as holidays, business trips, etc.) or is ordinarily resident in the UK (Contributions Regulations, reg. 145(1)(a)).