Political party in the United Kingdom in the context of Electoral Administration Act 2006

The Liberal Democrats, colloquially known as the Lib Dems, is one of the major political parties in the United Kingdom. Ideologically adhering to liberalism, it was founded in 1988. The party is based at Liberal Democrat Headquarters, which since September 2025 has been based at Buckingham Gate, in the Westminster area of Central London. The party's leader is Ed Davey. It is the third-largest party in the United Kingdom, with 72 members of Parliament (MPs) in the House of Commons. It has 75 members of the House of Lords, 5 in the Scottish Parliament, 1 in the Welsh Senedd, and around 3,200 local council seats. The party holds a twice yearly Liberal Democrat Conference, at which policy is formulated. In contrast to its main opponents, the Lib Dems grant all members attending Conference the right to vote on policy, under a one member, one vote system. As well as voting in the Conference Hall, the party allows its members to vote online for its policies and leadership elections. Members are also free to join organisations representing strands of party thinking, such as Liberal Reform and Social Liberal Forum, and for those under 30 years, Young Liberals.

In 1981, an electoral alliance was established between the Liberal Party, a group which descended from the 18th-century Whigs, and the Social Democratic Party (SDP), a splinter group from the Labour Party. In 1988, the parties merged as the Social and Liberal Democrats, adopting their present name a year later. Under the leaderships of Paddy Ashdown and Charles Kennedy, the party grew in the 1990s and 2000s, focusing its campaigns on specific seats and retained the third-largest party status in the House of Commons, although with significantly more seats than the predecessor Liberal Party. In the 1997 election, the Liberal Democrats doubled their seat count to 46. In 2010, under Nick Clegg's leadership, the Lib Dems were junior partners in the Conservative-led coalition government, in which Clegg served as deputy prime minister. Though it allowed the party to implement some of its policies, the coalition damaged its electoral standing; it lost 48 of its 56 MPs at the 2015 general election, which relegated it to fourth-largest party in the House of Commons. Under the leaderships of Tim Farron, Vince Cable and Jo Swinson, the party refocused as a pro-Europeanist party opposing Brexit. In the 2019 general election, the party garnered 11.5% of the vote on an anti-Brexit platform, but this did not translate into seat gains. However, the party's success was renewed under the leadership of Ed Davey, winning hundreds of councillors and 72 MPs in the 2024 general election, its highest result since 1923, and resuming its status as the third largest party in the House of Commons.

The Socialist Workers Party (SWP) is a political party in the United Kingdom. Founded as the Socialist Review Group (SRG) by supporters of Tony Cliff in 1950, it became the International Socialists in 1962 and the SWP in 1977. The party considers itself to be Trotskyist. Cliff and his followers criticised the Soviet Union and its satellites, calling them state capitalist rather than socialist countries.

The SWP has founded several fronts through which they have sought to coordinate and influence leftist action, such as the Anti-Nazi League in the late 1970s. It also formed an alliance with George Galloway and Respect, the dissolution of which in 2007 caused an internal crisis in the SWP. A more serious internal crisis emerged at the beginning of 2013 over allegations of rape and sexual assault made against a leading member of the party. The SWP's handling of these accusations against the individual known as "Comrade Delta", later identified as Martin Smith, led to a significant decline in the party's membership. It also led to a number of formal reviews which resulted in new procedures to support any member who experienced sexual harassment or other forms of oppressive behaviour.

The Social Democratic Party (SDP) was a centrist to centre-left political party in the United Kingdom. The party supported a mixed economy (favouring a system inspired by the German social market economy), electoral reform, European integration and a decentralised state while rejecting the possibility of trade unions being overly influential within industrial relations. The SDP officially advocated social democracy, and unofficially for social liberalism as well.

The SDP was founded on 26 March 1981 by four senior Labour Party moderates, dubbed the "Gang of Four": Roy Jenkins, David Owen, Bill Rodgers, and Shirley Williams, who issued the Limehouse Declaration. Owen and Rodgers were sitting Labour Members of Parliament (MPs); Jenkins had left Parliament in 1977 to serve as President of the European Commission, while Williams had lost her seat in the 1979 general election. All four had held cabinet experience in the 1970s before Labour lost power in 1979. The four left the Labour Party as a result of the January 1981 Wembley conference, which committed the party to unilateral nuclear disarmament and withdrawal from the European Economic Community. They also believed that Labour had become too left-wing, and had been infiltrated at the constituency party level by the Trotskyist Militant tendency, whose views and behaviour they considered to be at odds with the Parliamentary Labour Party and Labour voters.