List of UK by-elections

This is a list of parliamentary by-elections in the United Kingdom since 2010, with the names of the incumbent and victor and their respective parties. Where seats changed political party at the election, the result is highlighted: blue for a Conservative gain, red for a Labour gain, orange for a Liberal Democrat gain, purple for a UK Independence Party (UKIP) gain and grey for any other gain.

Where the cause of by-election is given as "resignation" or "seeks re-election", this indicates that the incumbent was appointed on his or her own request to an "office of profit under the Crown", either the Steward of the Chiltern Hundreds or the Steward of the Manor of Northstead. Accepting an office of profit under the Crown vacates the member's seat. This process is used because members of the House of Commons are not technically permitted to resign. A member who vacates their seat in this manner may stand for re-election.

There were 21 by-elections in the 2010–2015 Parliament. 14 were in seats held by Labour, four by the governing Conservatives, one by their coalition partners the Liberal Democrats and two by Sinn Féin, who do not take up their seats in the House of Commons. 17 by-elections were won by the incumbent party, Labour won a seat from the Conservatives and lost one to Respect, while UKIP gained two seats from the Conservatives after the incumbent MPs defected to the party and were re-elected. Six by-elections were a result of the death of the incumbent MP, all of whom represented Labour.

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