This is a list of parliamentary by-elections in the United Kingdom held between 1918 and 1931, with the names of the incumbent and victor and their respective parties.
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.
Some precise party allegiances are difficult to determine as during this Parliament the Liberal and Conservative Parties were both divided over whether or not to continue support for the Lloyd George Coalition Government.
It is not always clear just where an individual MP or officially endorsed candidate stood on the Coalition at the point of election and there are several who appear to have given ambiguous information at the time or to have switched wings once in Parliament.