A by-election is an election held in a single parliamentary constituency to fill a seat in the House of Commons that has become vacant between general elections. By-elections thus provide a mechanism to ensure continuous representation for all areas of the country.

While the voting process in a by-election is identical to a general election, their political character is distinct. They are sometimes seen as a barometer of the national mood and a mid-term verdict on the performance of the incumbent government, which typically performs poorly in these contests.

The causes of by-elections

A by-election is triggered when a sitting MP ceases to hold this position. This can happen for several reasons.

Resignation of an MP

MPs are technically forbidden from directly resigning their seats. Instead, an MP who wishes to stand down uses a constitutional convention whereby they are appointed to a historical “office of profit under the crown”, such as the crown steward and bailiff of the Chiltern Hundreds or the crown steward and bailiff of the Manor of Northstead. Accepting such an office automatically disqualifies them from being an MP, triggering a by-election.

Recall of an MP

The Recall of MPs Act 2015 allows voters to remove their MP and trigger a by-election. A recall petition is initiated if an MP is imprisoned, suspended from the House of Commons for at least 10 sitting days, or convicted of providing false expenses claims. If the petition is signed by 10% of eligible voters in the constituency within six weeks, the seat becomes vacant.

This process has successfully removed an MP four out of six times, leading to by-elections to replace Fiona Onasanya (2019), Chris Davies (2019), Margaret Ferrier (2023) and Peter Bone (2023). The recall of Scott Benton’s seat in Blackpool South 2024 was terminated early as the MP resigned two weeks after the petition began to be distributed.

Several MPs have resigned (secured appointment to the Chiltern Hundreds) when facing a sanction that would trigger the act’s provisions, namely: Owen Paterson (North Shropshire, 2021), Christian Matheson (City of Chester, 2021), Boris Johnson (Uxbridge and South Ruislip, 2023), Chris Pincher (Tamworth, 2023), and Mike Amesbury (Runcorn and Helsby, 2025).

Death of an MP

If a serving MP dies, their seat automatically becomes vacant. Five by-elections were held during the 2019-2024 parliament following the deaths of serving MPs. Those parliamentarians who passed away were Dame Cheryl Gillan (Chesham and Amersham, 2021); Sir David Amess (Southend West, 2021); James Brokenshire (Old Bexley and Sidcup, 2021); Jack Dromey (Birmingham, Erdington, 2022); and Tony Lloyd (Rochdale, 2024).

Campaigning or self-imposed by-elections

Some MPs have previously resigned their seats to trigger a self-imposed by-election, standing again in order to campaign on a specific issue.

In July 2008, the former shadow home secretary David Davis was comfortably re-elected in the Haltemprice and Howden by-election, which he had triggered as a protest against what he described as the “slow strangulation of fundamental British freedoms.”

In 2016, the Richmond Park by-election was triggered by incumbent Conservative MP Zac Goldsmith. Goldsmith resigned over the government’s proposal for a third runway at nearby Heathrow Airport; standing as an independent, he lost the self-imposed contest to Liberal Democrat candidate Sarah Olney.

In July 2026, Nigel Farage, the leader of Reform UK, resigned as an MP to call a by-election in his constituency of Clacton. It came as he faced questions concerning his finances. Farage said the by-election would give voters a chance to “stick two fingers up to the establishment”.

However, Farage’s sensational decision was met with a united front from the major parties, who successively took the decision not to stand in Clacton. This stance cleared the field for Count Binface, Britain’s best-known satirical candidate, to emerge as Farage’s most prominent challenger. Farage was returned as the MP for Clacton in August 2026, winning 22,239 votes (63.3%) against a field of 34 candidates – the largest ever assembled for a single UK parliamentary contest. Binface won 9,455 votes (26.9%)..

Self-imposed by-elections remain a relatively rare feature of modern British politics.

Other causes of by-elections

A by-election is required if an MP is convicted of a serious criminal offence resulting in a prison sentence of more than one year, or accepts a peerage to sit in the House of Lords.

A by-election is also required if an MP has been served a bankruptcy restrictions order, which is imposed by a court when an individual is said to have behaved dishonestly or irresponsibly in relation to their bankruptcy. These rules are set out under the Insolvency Act 1986 (as amended by the Enterprise Act 2002).

How a by-election is called

Once a seat becomes vacant, the chief whip of the party that previously held the seat will typically table a motion in the House of Commons to “move the writ.” This is a formal request for the commons speaker to issue a warrant to begin the election process. The speaker may also issue a writ during a recess period.

By convention, the writ is usually moved within three months of the vacancy occurring. This position was arrived at by the speaker’s conference on electoral law in 1973. Once the writ is issued, the by-election must take place between 21 and 27 working days later.

By-elections in the UK have been held on Thursdays since 1965. A notable exception occurred in 1978, when the Scottish town of Hamilton held its by-election on a Wednesday to avoid clashing with the kickoff of the World Cup in Argentina the following day.

There is nothing in statute law or in standing orders (commons rules) obliging the House to move a writ for a by-election. If a vacancy arises very close to a general election, it is usually left vacant to be contested at that election. In 2010, the seat of North-West Leicestershire, was left vacant for five months (awaiting the upcoming general election).

Voter behaviour at by-elections: a political barometer?

By-elections are closely watched by the media and political parties as they can reveal shifts in public opinion. However, the extent to which by-elections can be treated as a reliable political barometer is questionable.

With the fate of the national government not at stake, voters may feel more able to cast a “protest vote” against the incumbent government or engage in targeted tactical voting to support the candidate best placed to defeat the governing party.

The evidence of those by-elections fought in the 2019-2024 parliament speaks to this trend. Of the 23 by-elections held, the governing Conservative party only retained three seats and gained one, suffering some of the largest swings against a government in modern political history. Meanwhile, Labour won 13 by-elections, and the Liberal Democrats four.

Local issues can also play a more significant role than at a general election. In the 2023 Uxbridge and South Ruislip by-election, local opposition to the expansion of the ultra low emission zone (Ulez) by the Labour mayor of London, Sadiq Khan, was widely seen as crucial to the Conservative victory.

Voter turnout in by-elections is generally lower than in general elections.

The lower turnout in by-elections can make “differential turnout” among highly motivated voters decisive. This dynamic can help explain why governing parties often perform poorly in by-elections, as long-standing critics of the government – particularly those who sense an opportunity to secure a news-making scalp – are typically more motivated to turn out than its supporters.

Moreover, George Galloway, the firebrand former Labour MP, has achieved significant success in mobilising Muslim voters in constituencies where they form a significant share of the electorate. By focusing on issues that resonate strongly within the local Muslim community, Galloway can ensure that these voters make up a disproportionate share of those who turn out at a by-election.

How many by-elections take place during a typical parliament?

• Between the 2019 and 2024 general elections, there were 23 by-elections
• Between 2017 and 2019, there were five by-elections.
• Between 2015 and 2017, there were 10 by-elections.
• Between 2010 and 2015, there were 21 by-elections.
• Between 2005 and 2010, there were 14 by-elections.

The ‘super thursday’ by-elections held on 20 July 2023

On 20 July 2023, a trio of parliamentary by-elections saw the available seats apportioned among the three main parties – with all of the Labour, Conservative and Liberal Democrat parties securing wins. The contests, held simultaneously in Selby and Ainsty, Somerton and Frome, and Uxbridge and South Ruislip, were triggered by the resignations of Conservative MPs.

In Selby and Ainsty (North Yorkshire), triggered by Nigel Adams’ resignation, the Labour party achieved a historic victory. Keir Mather overturned a Conservative majority of 20,137 from the 2019 general election, winning with a majority of 4,161 on a remarkable swing of 23.7 points – one of the largest swings to Labour from the Conservatives since the Second World War.

In Somerton and Frome (Somerset), following David Warburton’s resignation, the Liberal Democrats secured an even more dramatic win. Sarah Dyke overturned a Conservative majority of 19,213, winning by 11,008 votes on a swing of 29 points. The result validated the Liberal Democrats’ electoral strategy of targeting Conservative strongholds in the so-called “blue wall”.

The only consolation for the government came in Uxbridge and South Ruislip (London), which had been vacated by the former prime minister, Boris Johnson. The Conservative candidate, Steve Tuckwell, held the seat by a margin of just 495 votes. The significantly smaller swing against the Conservatives here (6.7) was widely attributed to local opposition to the planned expansion of Ulez by Sadiq Khan as London mayor.

All of Adams, Warburton and Johnson had stood down in controversial circumstances. At the time of his resignation, Warburton had been facing accusations of sexual harassment and drug abuse – allegations which befit a narrative of Conservative “sleaze”.

Johnson, meanwhile, resigned in protest at the commons privileges committee’s report into ‘Partygate’. The former prime minister had been given advanced sight of the report, which found he misled the House. Johnson stepped down as an MP rather than face a likely recall petition.

Adams, a strong supporter of the ex-PM, resigned alongside Johnson in solidarity and protest.

The Selby and Somerton contests spoke to a remarkably developed “get the Tories out” fervour. The Uxbridge result offered some relief for the embattled prime minister, Rishi Sunak; however, the outcome reflected the contest’s distinctive character – rather than any meaningful revival in the Conservative Party’s fortunes.

Nevertheless, Sunak seized on the result, journeying to Uxbridge to bask in his party’s by-election victory. The contest may also have marked a turning point for the government’s green and environmental policy. Sunak subsequently doubled down on his opposition to ULEZ-style measures and scaled back the government’s net zero commitments.

But this initiative failed to revive his party’s position. The Conservatives won 121 seats at the 2024 general election, down 251 – belated proof that the Selby and Somerton contests were a truer reflection of the public mood after all.

Steve Tuckwell lost his Uxbridge and South Ruislip seat at the 2024 election, having served less than a year in parliament.

By-elections in the 2024 parliament

Overview:

• Total by-elections held: 6
• Total seats that changed hands: 3
• Seats lost by the governing Labour Party: 2
• Seats won by the governing Labour Party: 1 (1 held)
• Successful recall petitions leading to a by-election: 0

Outcomes and details:

• 1 May 2025 – Runcorn and Helsby | Winning party: Reform UK (Gain from Labour) | Winning candidate: Sarah Pochin
• 26 February 2026 – Gorton and Denton | Winning party: Green Party (Gain from Labour) | Winning candidate: Hannah Spencer
• 18 June 2026 – Makerfield | Winning party: Labour (Retained) | Winning candidate: Andy Burnham
• 18 June 2026 – Aberdeen South | Winning party: Conservative (Gain from SNP) | Winning candidate: Douglas Lumsden
• 18 June 2026 – Arbroath and Broughty Ferry | Winning party: SNP (Retained) | Winning candidate: Lara Bird
• 13 August 2026 – Clacton | Winning party: Reform UK (Retained) | Winning candidate: Nigel Farage

By-elections in the 2019 parliament

Overview:

• Total by-elections held: 23
• Total seats that changed hands: 14
• Seats lost by the governing Conservative Party: 11
• Seats won by the governing Conservative Party: 4 (3 held)
• Successful recall petitions leading to a by-election: 2

Outcomes and details:

• 6 May 2021 — Hartlepool | Winning party: Conservative (Gain from Lab) | Winning candidate: Jill Mortimer
• 13 May 2021 — Airdrie and Shotts | Winning party: SNP (Hold) | Winning candidate: Anum Qaisar-Javed
• 17 June 2021 — Chesham and Amersham | Winning party: Liberal Democrats (Gain from Con) | Winning candidate: Sarah Green
• 1 July 2021 — Batley and Spen | Winning party: Labour (Hold) | Winning candidate: Kim Leadbeater
• 2 December 2021 — Old Bexley and Sidcup | Winning party: Conservative (Hold) | Winning candidate: Louie French
• 16 December 2021 — North Shropshire | Winning party: Liberal Democrats (Gain from Con) | Winning candidate: Helen Morgan
• 3 February 2022 — Southend West | Winning party: Conservative (Hold) | Winning candidate: Anna Firth
• 3 March 2022 — Birmingham, Erdington | Winning party: Labour (Hold) | Winning candidate: Paulette Hamilton
• 23 June 2022 — Wakefield | Winning party: Labour (Gain from Con) | Winning candidate: Simon Lightwood
• 23 June 2022 — Tiverton and Honiton | Winning party: Liberal Democrats (Gain from Con) | Winning candidate: Richard Foord
• 1 December 2022 — City of Chester | Winning party: Labour (Hold) | Winning candidate: Samantha Dixon
• 15 December 2022 — Stretford and Urmston | Winning party: Labour (Hold) | Winning candidate: Andrew Western
• 9 February 2023 — West Lancashire | Winning party: Labour (Hold) | Winning candidate: Ashley Dalton
• 20 July 2023 — Selby and Ainsty | Winning party: Labour (Gain from Con) | Winning candidate: Keir Mather
• 20 July 2023 — Uxbridge and South Ruislip | Winning party: Conservative (Hold) | Winning candidate: Steve Tuckwell
• 20 July 2023 — Somerton and Frome | Winning party: Liberal Democrats (Gain from Con) | Winning candidate: Sarah Dyke
• 5 October 2023 — Rutherglen and Hamilton West | Winning party: Labour (Gain from SNP) | Winning candidate: Michael Shanks
• 19 October 2023 — Mid Bedfordshire | Winning party: Labour (Gain from Con) | Winning candidate: Alistair Strathern
• 19 October 2023 — Tamworth | Winning party: Labour (Gain from Con) | Winning candidate: Sarah Edwards
• 15 February 2024 — Wellingborough | Winning party: Labour (Gain from Con) | Winning candidate: Gen Kitchen
• 15 February 2024 — Kingswood | Winning party: Labour (Gain from Con) | Winning candidate: Damien Egan
• 29 February 2024 — Rochdale | Winning party: Workers Party of Britain (Gain from Lab) | Winning candidate: George Galloway
• 2 May 2024 — Blackpool South | Winning party: Labour (Gain from Con) | Winning candidate: Chris Webb