The Labour Party is a political party in the United Kingdom. Founded in the early 20th century, it has been since the 1920s the principal party of the centre-left in Great Britain (England, Scotland and Wales) but not in Northern Ireland, where the Social Democratic and Labour Party occupies a roughly similar position on the political spectrum, though people in Northern Ireland can still join the party. It has formed the national government of the United Kingdom since 1997. It is also the largest party in the Welsh Assembly Government in Wales and the second largest party in the Scottish Parliament. It holds the London mayoralty and is represented in the European Parliament. Its current leader is Gordon Brown.

The Labour Party surpassed the Liberal Party as the main opposition to the Conservatives in the early 1920s. It has had several spells in government, first as minority governments under Ramsay MacDonald in 1924 and 1929-31, then as a junior partner in the wartime coalition from 1940-1945, and then as a majority government, under Clement Attlee in 1945-51 and under Harold Wilson in 1964-70. Labour was in government again in 1974-79, under Wilson and then James Callaghan, though with a precarious and declining majority.

New Labour won a landslide 179 seat majority in the 1997 general election under the leadership of Tony Blair, its first general election victory since October 1974 and the first general election since 1970 in which it had exceeded 40% of the popular vote. The Labour Party's large majority in the House of Commons was slightly reduced to 167 in the 2001 general election and more substantially reduced to 66 in 2005.