What is a by-election?

A by-election is an election held in one constituency between general elections. It fills a seat in the House of Commons that has become empty. It happens when an MP dies, resigns, is disqualified or loses their seat through a recall petition. Only voters in that area take part.

When a seat becomes vacant, the party that held it usually decides when to start the process. The Commons agrees a motion, called a writ, and the election normally takes place within a few weeks. MPs cannot simply resign. Instead they are appointed to an old paid post of the Crown, the Chiltern Hundreds or the Manor of Northstead, which disqualifies them. A by-election can also follow a successful recall petition, where at least 10% of voters sign to remove an MP. By-elections use first past the post, just like general elections. They are often seen as a test of the government's popularity, and governing parties often do badly in them. Each lost seat makes a government's majority smaller. Turnout is usually lower than at a general election.