By-election dates announced for Boris Johnson and Nigel Adams' constituencies after they quit as MPs

The by-election for Boris Johnson's Uxbridge and South Ruislip seat has been set for 20 July.

It follows the dramatic resignation of the former prime minister, who quit on Friday in advance of the report into whether he lied to MPs about lockdown parties in Downing Street.

Two of Mr Johnson's closest allies - Nadine Dorries and Nigel Adams - joined him in walking out the door, meaning the Tories face three electoral tests at a time when they are trailing Labour in the national polls.

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The by-election in Mr Adams's seat of Selby and Ainsty will also be held on Thursday 20 July.

However, Sky News understands that despite announcing her resignation, Ms Dorries plans to prolong the pain for the prime minister by standing down at a later date - creating the potential for an autumn by-election.

She claimed on Twitter that she is seeking information about her ennobling being blocked before she leaves the Commons.

The bombshell report into whether Mr Johnson miseld the Commons over his denials of gatherings in Downing Street doing COVID ended up recommending a suspension of 90 days - a higher than expected number due in part to Mr Johnson's reaction to finding out what his fate was.

A ban of 10 days is what is necessary to trigger a recall petition and a potential by-election.

All eyes are particularly on Mr Johnson's west London constituency, where the Tories had a 53% share of the vote at the last general election in 2019.

The seat was in Labour's top 100 targets at the next election even before Mr Johnson's resignation, and polling suggests the opposition has a 14-point lead.

Danny Beales, the Labour candidate, insisted he is not taking "anything for granted" as he kickstarted his campaign on Saturday, less than 24 hours after Mr Johnson quit.

The Tories are defending a majority of over 7,000 in Uxbridge, a seat which they have held since 2010 and which Mr Johnson first won in 2015.

To overturn that majority Labour needs a swing in the share of the vote of 7.5 percentage points - in other words, eight in every 100 people who voted Tory in 2019 would need to switch to Labour.

Labour needs a much bigger swing in Mr Adams and Ms Dorries's constituencies, where the Conservatives are cushioned by majorities of over 20,000.

Mr Adams has vowed to help deliver a victory for the Tories in his North Yorkshire seat.

The Lib Dems see Ms Dorries' mid-Bedfordshire constituency as a winnable target after having achieved massive swings to take so-called Blue Wall seats in the south of England during the local elections.

Both Mr Johnson and Mr Adams formalised their resignations on Monday, beginning the process so the by-elections can go ahead before the summer recess in July.

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Under parliamentary convention, sitting MPs cannot technically resign - unless they die or are expelled, they must become disqualified if they wish to retire before the end of a parliament.

They do this by applying for a paid office of the Crown which disqualifies them from holding a Commons seat.

Mr Johnson accepted the post of crown steward and bailiff of the Chiltern Hundreds, while Mr Adams accepted the alternative title of steward and bailiff of the Manor of Northstead.

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Simon Hart, the Conservative chief whip, yesterday kickstarted the process by moving the writ in parliament, which asks MPs whether they agree to a by-election.

Once they agree, the Speaker issues a warrant to a senior civil servant who sends the writ to the returning officer, who will be responsible for overseeing the by-election in that seat.