This is a list of parliamentary by-elections in the United Kingdom, with the names of the incumbent and victor and their respective parties. Where seats changed political party at the election, the result is highlighted: red for a Labour gain, blue for a Conservative gain, orange for a Liberal gain, yellow for an SNP gain, green for a Plaid Cymru gain and grey for any other gain.

Resignations

Where the cause of by-election is given as "resignation" or "seeks re-election", this indicates that the incumbent was appointed on his or her own request to an "office of profit under the Crown", either the Steward of the Chiltern Hundreds or the Steward of the Manor of Northstead. These appointments are made as a constitutional device for leaving the House of Commons, whose Members are not permitted to resign.

By-elections

{| class="wikitable"

October 1974–1979 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

February–October 1974 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

1970 – February 1974 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

1966–1970 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

1964–1966 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

1959–1964 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

1955–1959 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

1951–1955 Parliament

!By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause

1950–1951 Parliament

No seats changed hands during this Parliament. !By-election !! Date !! Incumbent !! colspan=2 | Party !! Winner !! colspan=2 | Party !! Cause