Note: This chart is a available in the spreadsheet that can be downloaded below.

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. There have been four by-elections in the current 2017 Parliament.

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 on UK Election Statistics: 1918–2010 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.


Please send any comments or corrections to the Parliament & Constitution Centre. Suggestions for new lists welcomed.

Related posts

  • Constituency boundary reviews and the number of MPs

    Parliamentary constituency boundaries are reviewed periodically by independent Boundary Commissions. This House of Commons Library briefing summarises the current rules and procedures for boundary changes and how they have changed over time. It also gives an overview how the number of MPs has reached the current level of 650.

    Constituency boundary reviews and the number of MPs
  • Parliamentary boundary reviews: public consultations

    Parliamentary constituency boundaries reviews are undertaken by independent Boundary Commissions. There are four Commissions, one for each of the nations of the UK. The Commissions rely on public feedback to refine their proposals. This briefing summarises the consultation process

    Parliamentary boundary reviews: public consultations