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Chart showing by-elections since 1945

When do by-elections happen?

A by-election occurs when a seat in the House of Commons becomes vacant during the lifetime of a Parliament (ie between general elections), because the sitting MP dies, resigns, is elevated to the peerage, or becomes ineligible to sit for some other reason. 

Resignations from the House of Commons

Under a Resolution of the House of 2 March 1623, MPs cannot directly resign their seats. Therefore, an MP wishing to resign must be appointed to one of two nominal offices of profit under the Crown. See the Library briefing Appointments to the Chiltern Hundreds and Manor of Northstead Stewardships since 1880.

Further information

The by-elections page of the Parliament website provides detailed information on results, including the number of votes cast and percentage share of the vote.

See the Commons briefing, UK Election Statistics: 1918-2021: A century of elections for a list of all by-elections in Great Britain and Northern Ireland.

Parliament: facts and figures

This series of publications contains data on various subjects relating to Parliament and Government. Topics include legislation, MPs, select committees, debates, divisions and Parliamentary procedure.


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