In the United Kingdom the term "unionist' may indicate support for either;
- the 1707 Act of Union between Scotland and England or,
- the 1800 Act of Union between Ireland (and more recently Northern Ireland) and Great Britain.
Nationally, the full name of the Conservative Party is the Conservative and Unionist Party.
In Northern Ireland (see Unionism in Ireland and Ulster loyalism), active parties include:
- Democratic Unionist Party (DUP) - The larger of the two main unionist political parties in Northern Ireland; founded by Ian Paisley and currently led by Peter Robinson. The largest party in the Northern Ireland Assembly and the fourth-largest party in the House of Commons of the United Kingdom
- Protestant Unionist Party - formed by Ian Paisley in 1966 out of the Ulster Protestant Action (UPA) movement. It was the forerunner of the Democratic Unionist Party and disbanded in 1971 with the DUP's formation
- Ulster Unionist Party (UUP) - The smaller and more moderate of the two main unionist political parties in Northern Ireland. It governed Northern Ireland between 1921 and 1972 as the sole Unionist party.
- Ulster Conservatives and Unionists – New Force (Conservatives and Unionists) - electoral alliance between the UUP and the Conservatives in Northern Ireland, the Northern Ireland arm of the Conservative Party
- Progressive Unionist Party (PUP), minor loyalist party formed in 1979
- Ulster Unionist Labour Association (or Labour Unionist Party)
Defunct parties include:
- Independent Unionist Association (or Independent Unionist Party) - existed from 1937 to late 1940s. Consisted of a disparate group of independent Unionists, and included Tommy Henderson, member of the House of Commons of Northern Ireland
- Vanguard Unionist Progressive Party (Ulster Vanguard), existed from 1973 and 1978; far-right party
- Unionist Party of Northern Ireland, existed from 1974 and 1981
- United Ulster Unionist Party, existed from 1975 and 1982, splinted from the Vanguard Progressive Unionist Party due to a disagreement over power-sharing
- Ulster Popular Unionist Party, existed from 1980 to 1995; led by James Kilfedder
- UK Unionist Party, existed 1995 to 2008
- Northern Ireland Unionist Party, existed 1999 to 2008
In Scotland (see Unionism in Scotland):
- Scottish Conservative and Unionist Party, full name of what is usually referred to as the Scottish Conservative Party
- Scottish Unionist Party (1986), Scottish minor party of traditionalist unionists disillusioned with the Conservative government's signing of the Anglo-Irish Agreement
- Unionist Party (Scotland), centre-right party that existed between 1912 and 1965, dominant force in Scottish politics until the late 1950s
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