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UK parliamentary by-elections

A UK parliamentary by-election happens when a seat in the House of Commons becomes vacant between general elections.

A seat can become vacant when an MP:

  • resigns or dies
  • is declared bankrupt
  • takes a seat in the House of Lords
  • is convicted of a serious criminal offence
  • is recalled by their constituents following a successful recall petition

A by-election does not have to take place if an MP changes political party.

Who can vote in these elections

To vote at a UK parliamentary by-election you must be registered to vote and:

  • be 18 years of age or over on polling day
  • be a British, Irish or qualifying Commonwealth citizen
  • be resident at an address in the UK (or a UK citizen living abroad who has been registered to vote in the UK in the last 15 years)
  • not be legally excluded from voting

The following people cannot vote in a UK Parliament election:

  • members of the House of Lords
  • EU citizens (other than the Republic of Ireland, Cyprus and Malta) resident in the UK
  • anyone other than British, Irish and qualifying Commonwealth citizens
  • convicted persons detained in pursuance of their sentences, excluding contempt of court (though remand prisoners, unconvicted prisoners and civil prisoners can vote if they are on the electoral register)
  • anyone found guilty within the previous five years of corrupt or illegal practices in connection with an election

Find out more information about who is eligible to vote.

Voting in these elections

UK parliamentary by-elections use the first past the post system. You will only be able to vote for one candidate, by putting a cross [X] in the box next to your choice. 

MPs usually sit for a five-year term. However, when a MP is elected through a by-election, they will serve for the remainder of the original term. For example, if a by-election takes place one year after a general election, the MP who is elected will serve for four years until the next general election. 

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