Parliaments of England, Scotland, Ireland and the various unions of these Kingdoms had been assembled since the medieval period, though these bodies only gradually evolved to be democratically elected by the populace and records are incomplete.
England and Wales had numerous "rotten boroughs" with tiny and tightly controlled electorates until the Reform Act 1832.
Among the most significant aspects of historical elections which are no longer present are: Since 1945, the legal and general political situation regarding by-elections has been broadly stable, allowing for meaningful comparison of records.
[2] At the 1892 Cirencester by-election a majority of 3 for the Unionists was overturned on petition, where it was found that both candidates had an equal number of votes.
It is highly unusual for a by-election to attract a higher turnout in a seat than the previous general election.
During the Second World War the electoral register was not kept up to date despite significant population movements, especially in the London area (which contains all three constituencies in the first list below).
Former Labour cabinet minister Tony Benn contested no fewer than four by-elections during his career, topping the poll on each occasion: Bristol South East in 1950, 1961 and 1963, and Chesterfield in 1984.
Former cabinet minister and European Commissioner Roy Jenkins fought two different by-elections for the Social Democratic Party only eight months apart.
John Bickley of UKIP contested three by-elections (all in Greater Manchester) within two years - Wythenshawe and Sale East in February 2014, Heywood and Middleton in October 2014 and Oldham West and Royton in December 2015.
On 23 January 1986, Wesley Robert Williamson (who changed his name to Peter Barry) stood in four simultaneous by-elections in Northern Ireland.
Arthur Henderson was distinguished in being successful in no fewer than five by-elections in different seats, in Barnard Castle, Widnes, Newcastle upon Tyne East, Burnley, and Clay Cross.
Notes: 1 by-election gain lost at the subsequent general election 2 by-election gain held at the subsequent general election Until the Re-election of Ministers Acts 1919 and 1926 there were many cases of members having to seek re-election on appointment to ministerial office.
In eight instances since 1900 they were unsuccessful: Note this list covers completed service only; it excludes any current MPs.
Notes See Baby of the House of Commons Debuts in Parliament: Comebacks to Parliament: In defence of a previously held seat: The first woman to be elected in a by-election was Nancy Astor, who succeeded her husband at the 1919 Plymouth Sutton by-election, becoming the first woman to take her seat in the House of Commons.
The first by-election victor (and first ever MP) to be an adherent of the Eastern Orthodox Church was The Honourable Frederick North who was elected in 1792 for Banbury (to succeed his brother who had entered the House of Lords), having converted to the faith the previous year.
Those known to have been disabled when entering parliament at by-elections are rarer and include: 1 Hilton Dawson, Thelma Walker, and Paul Williams 2 Conservative MPs David Davis and Walter Sweeney The usual causes of by-elections – death or resignation – mean that incumbent MPs are rarely candidates.
Typically, this only occurs if an MP deliberately triggers a by-election to get a mandate for a party change, or to bring a particular issue to public attention.
Labour's longest lean stretch was almost 18 years, between gaining the 1939 Brecon and Radnorshire by-election and the 1957 Lewisham North by-election.1 As of 22 February 2025, the most recent gains for each currently active party were: Notes 1 The Labour Party were the official opposition in the Parliament elected in 1935, but after the major parties agreed an electoral truce on the outbreak of war in 1939, they did not contest any Conservative or Liberal seats for the remainder of the Parliament, a period of six years, and were members of the wartime coalition government between May 1940 and May 1945.
However, the Anti H-Block party, an Irish Republican group that merged into Sinn Féin, gained Fermanagh and South Tyrone in the April 1981 by-election (43 years, 10 months and 13 days ago).
The span of 14 years, 10 months and 8 days is the longest period without a by-election defeat for either of the two main parties.
Motivations include attempting to divide opponents' resources and getting bad news (expected losses) out of the way.
Very occasionally, a scheduled by-election may be overtaken by the calling of a general election and the dissolution of Parliament, in which case the poll is countermanded by the Returning Officer.
In 2017 the Manchester Gorton by-election was cancelled by a Motion in the House of Commons following the calling of the 2017 United Kingdom general election.
By the end of the Parliament, the following Sinn Féin MPs had died without being replaced: Pierce McCan (East Tipperary) of influenza on 6 March 1919, Terence MacSwiney (Mid Cork) following a hunger strike in Brixton prison on 25 October 1920, Frank Lawless (North Dublin) as a result of a riding injury on 16 April 1922, Joseph McGuinness (Longford) on 31 May 1922, Cathal Brugha (Waterford) in action during the Irish Civil War on 7 July 1922, Harry Boland (South Roscommon) shot while being arrested on 2 August 1922, Arthur Griffith (East Cavan and North West Tyrone) on 12 August 1922, and Michael Collins (South Cork assassinated on 22 August 1922).
These records show the rare occasions when the official Opposition failed to hold on to a seat they had won at the previous General election.
On rare occasions a party has failed to overturn an incumbent in the by-election yet has gone on to gain the seat at the subsequent general election.
Minor parties without representation in the House of Commons which saved their deposit: Notes: Labour joined the Liberal Democrats and the Greens in not contesting the 2022 Southend West by-election, out of respect following the murder of the previous MP, Sir David Amess.
The Conservatives, Liberal Democrats, UKIP, and Green Party declined to run candidates in the 2016 Batley and Spen by-election, due to the circumstances regarding the murder of the previous MP, Jo Cox.
The by-election was a single-issue election in regards to government security policy, in which the Liberal Democrats supported the Conservative candidate.
It is also unusual for the principal opposition party to suffer a significant reverse in its share of the vote or ranking.