TCTM02805 - Entitlement: Tax credits and European Law: The principle of single application of legislation

The basic principle is that a person at any given point in time can be subject to the legislation of a single Member State (MS) only.

A person who is pursuing an activity as an employed or self employed person in a MS, is subject to the legislation of that MS, even if they live in another MS;
A civil servant is subject to the legislation of the MS who employs him/her;
A person receiving unemployment benefits from the MS where they live is subject to the legislation of that MS;
Where a person is normally employed or self employed on a vessel at sea flying a flag of a MS, the person is subject to the legislation of that MS.
Where a person is employed on a vessel flying the flag of a MS, but the employer’s place of business or registered office is located in another MS, and the worker also resides in that MS, the person is subject to the legislation of the MS where he resides.
Where none of the above rules apply, a person shall be subject to the legislation of the MS where they live.

Where a person pursues activity as an employed or self employed person in more than one MS, the following rules apply:

If a substantial part of his activity takes place in the MS of residence, he will be subject to the legislation of that MS.
If a substantial part of his activity does not take place in the MS of residence, he will be subject to the MS in which the registered office or place of business of his employer, or for the self employed, the MS in where the main activity takes place.
‘Substantial’, here means 25 per cent or more.

Tax Credits Technical Manual