This article lists political parties in the United Kingdom.
Before the mid-19th century politics in the United Kingdom was dominated by the Whigs and the Tories. These were not political parties in the modern sense but somewhat loose alliances of interests and individuals. The Whigs included many of the leading aristocratic dynasties committed to the Protestant succession, and later drew support from elements of the emerging industrial interests and wealthy merchants, while the Tories were associated with the landed gentry, the Church of England and the Church of Scotland.
By the mid 19th century the Tories had evolved into the Conservative Party, and the Whigs had evolved into the Liberal Party. In the late 19th century the Liberal Party began to lean towards the left, and many of the heirs of the Whig tradition became Liberal Unionists and moved closer to the Conservatives on many of the key issues of the time.
The Liberals and Conservatives dominated the political scene until the 1920s, when the Liberal Party declined in popularity and suffered a long stream of resignations. It was replaced as the main anti-Tory opposition party by the newly emerging Labour Party, which represented an alliance between the labour movement, organised trades unions and various Socialist societies.
Since then the Conservative and Labour parties have dominated British politics, and have alternated in government ever since. However, the UK is not quite a two-party system as other parties have significant support. The Liberal Democrats were the third largest party until the 2015 general election when they were overtaken by the Scottish National Party in terms of seats and by UKIP in terms of votes.