In British politics, the term affiliated trade union refers to a trade union that has an affiliation to the Labour Party (UK).

The Party was created by the trade unions and socialist societies in 1900 (as the Labour Representation Committee). Since then, the unions have retained close institutional links with the Party, although these links have been weakened significantly over time.

Affiliation means that the unions pay an affiliation fee to the Labour Party; in return, they and their members receive the privileges of affiliated membership. Unions select twelve of the thirty-two members of the Labour National Executive Committee and elect fifty per cent of the delegates to Labour Party Conference. In many cases, local union branches also affiliate to Constituency Labour Parties (CLPs).

Members of the unions may opt out of the affiliation, so that the member is not allowed to take part in any Labour Party ballots (such as the leadership election) in which other members of the affiliated union are involved.