This list notes the number of by-elections by session since 1945-46 and also gives the results for by-elections since 2005.
UK parliamentary by-elections since 1945 (147 KB , PDF)
Note: This chart is a available in the spreadsheet that can be downloaded below.
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.
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.
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.
UK parliamentary by-elections since 1945 (147 KB , PDF)
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.
Constituencies are reviewed periodically by independent Boundary Commissions, one for each part of the UK. This briefing outlines how the public can get involved in the consultation stages.
A briefing paper on the Anglo-Irish Treaty, 1921
