This is a list of notable defections or splits made by members of Parliament in the United Kingdom. They must have either been sitting MPs or MEPs at the time, or in between sessions.

• 1904: Winston Churchill - from the Conservative Party to the Liberal Party
• 1920: Oswald Mosley - from the Conservative Party to Independent.
• 1924: Oswald Mosley - from Independent to the Labour Party
• 1924: Winston Churchill - formally a member of the Liberal Party, elected as a 'Constitutionalist', joined the Conservative Party
• 1931: Oswald Mosley - from the Labour Party to the New Party
• 1931: Ramsay Macdonald - from the Labour Party, established National Labour with his supporters
• 1962: Alan Brown - from the Labour Party to the Conservative Party
• 1976: John Stonehouse - from the Labour Party to the English National Party
• 1977: Reginald Prentice - from the Labour Party to the Conservative Party
• 1981: The Gang of Four: Shirley Williams, David Owen, Roy Jenkins and Bill Rodgers, from the Labour Party to form the Social Democratic Party; a total of 28 Labour and 1 Conservative MPs eventually joined
• 1995: Alan Howarth - from the Conservative Party to the Labour Party
• 1995: Emma Nicholson - from the Conservative Party to the Liberal Democrats
• 1997: Peter Temple-Morris - from the Conservative Party to sit as a 'One Nation Conservative; joined the Labour Party in 1998
• 1999: Shaun Woodward - from the Conservative Party to the Labour Party
• 2000: Bill Newton Dunn MEP - from the Conservatives to the Liberal Democrats
• 2001: Paul Marsden - from the Labour Party to the Liberal Democrats
• 2002: Andrew Hunter - from the Conservatives to being an Independent supporter of the Democratic Unionist Party (took the party whip in 2004)
• 2004: Jeffrey Donaldson - from the Ulster Unionist Party to the Democratic Unionist Party
• 2004: Robert Kilroy-Silk MEP - from the UK Independence Party to Veritas
• 2005: Robert V. Jackson - from the Conservative Party to the Labour Party

See also

• British political scandals