By-elections 2023: a simple guide to three polls on 20 July

Voters go to the polls on Thursday 20 July in three by-elections which will provide a major test of Rishi Sunak's authority.

The prime minister faces the possibility of losing three Conservative seats after their previous MPs left the political stage.

A poor performance by the Tories would raise new questions about Mr Sunak's ability to revive the Tories' political fortunes in time for a general election expected next year.

There are also questions to be answered about how well Labour and the Liberal Democrats are doing.

Three by-elections are taking place: in the west London constituency of Uxbridge and South Ruislip, Selby and Ainsty in North Yorkshire, and the Somerset seat of Somerton and Frome.

A by-election is the process for electing a new member of parliament when a seat in the House of Commons becomes vacant outside a general election. This can happen, for example, when an MP dies or resigns.

These by-elections are the result of three MPs stepping down in the wake of separate controversies.

Former Prime Minister Boris Johnson, who was MP for Uxbridge and South Ruislip, announced he would resign his seat after he was handed a report from a committee of MPs investigating whether he lied to Parliament about Partygate - the series of Covid lockdown parties in Downing Street. Those MPs recommended a tough punishment that could have led to him facing a by-election.

Nigel Adams, MP for Selby and Ainsty, was a close ally of Mr Johnson and announced he would be stepping down a day later. His move came amid controversy over Mr Johnson's resignation honours list, on which Mr Adams did not appear.

The third by-election in Somerton and Frome came about because its former MP, David Warburton, resigned after admitting taking cocaine. Mr Warburton has also been accused of making unwanted advances towards two women, which led to his suspension from the Conservative Party in April last year. A re-investigation has been ordered into the allegations of sexual misconduct, which he denies.

The mood among Conservative MPs going into these by-elections is low. Expectations lean towards losing all three contests.

Despite this, there is little appetite for yet another leadership challenge, BBC political correspondent Nick Eardley says.

But three defeats would re-ignite the debate about what is going wrong for the Tory Party and how to fix it.

With sustained, large leads in national opinion polls, Labour wants to show it is on course to win the next general election and has enough momentum to take seats from the Conservatives in by-elections.

Sir Keir Starmer's party has particularly targeted Uxbridge and South Ruislip, and Selby and Ainsty.

But in Somerton and Frome, the Liberal Democrats were well ahead of Labour in the 2019 general election, and are expected to be the main challengers.

Sir Ed Davey's party will be looking to build on a series of by-election victories since 2021, when it has overturned big Tory majorities in Chesham and Amersham, North Shropshire, and Tiverton and Honiton.