Social Democratic Party (UK, 1990–present)

The Social Democratic Party (SDP) is a political party in the United Kingdom founded in 1990. It traces its origin to the Social Democratic Party, established in 1981 by four former LabourMPs who became known as the Gang of Four. The original party merged with the Liberal Party in 1988 to form the Liberal Democrats, but a breakaway faction led by David Owen existed as "the continuing SDP" until its dissolution in June 1990. The current SDP was subsequently formed by members who opposed the dissolution.

Ideologically, the SDP combines social democracy with cultural conservatism, and it advocates for a social market economy. Its policies include public ownership of the railways and utilities, a broader welfare state, greater public investment, reduced inequality and increased defence spending. It also campaigns for a selective education system, tougher criminal justice, restrictions on immigration, and the withdrawal from supranational institutions including the European Court of Human Rights, the Council of Europe, and the 1951 United Nations refugee convention.

The SDP has no representation in the House of Commons. It has held seats in local government, including all three seats in the Middleton Park ward of Leeds. In 2018, Patrick O'Flynn became the party's first and only Member of the European Parliament after defecting from UKIP. The following year, journalist Rod Liddle joined the party.

William Clouston served as party leader from 2018 until his resignation in 2026. During his tenure, the SDP initially fielded 20 candidates in the 2019 general election, growing to 122 candidates in the 2024 general election, where it had entered into an electoral pact with Reform UK in some constituencies. The SDP has also contested mayoral elections, including the 2024 London mayoral election with candidate Amy Gallagher, and the 2024 South Yorkshire mayoral election, in which the party's candidate received 20,835 votes (7.6%), a 3.7% increase on the previous result.