He was sentenced to 10 weeks behind bars after he pleaded guilty to the assault by beating of 45-year-old Paul Fellows in Frodsham, Cheshire, in the early hours of 26 October.
He announced his resignation as MP for Runcorn and Helsby in a social media post on Monday, describing the assault as a “deeply regrettable incident” for which he had “rightly been punished”.
“I am sincerely sorry to Paul Fellows, my family, colleagues and constituents,” he added.
A by-election will now be triggered in Runcorn and Helsby, where constituents will vote to elect a new MP.
Image: Mike Amesbury leaving Chester Crown Court in February. Pic: PA
By-election a ‘big test’ for PM
It will be the first by-election since Sir Keir Starmer became prime minister, in what Sky News’ political correspondent Liz Bates said would be a “big test” in a seat where Reform UK came second last year.
“Losing it would be an unmitigated disaster given the 14,000 majority achieved last time round,” said Bates.
Amesbury came first in Runcorn and Helsby with 22,358 votes at the 2024 general election – equating to 52.9% of the electorate.
Reform UK came in second with 7,662 votes (18.1%) and the Tories in third with 6,756 votes (16%).
Reform has yet to announce a candidate, but Karen Shore, the deputy leader of Cheshire West and Chester Council, will run for Labour.
The Conservatives have opted for Sean Houlston, a membership services manager for the National Federation of Builders.
Image: Sir Keir Starmer’s government has been polling very badly indeed. Pic: PA
When will the by-election be?
Under parliamentary procedure, an MP cannot simply resign but must be disqualified from holding their seat.
To do this, they must apply for a role in the paid office of the Crown, meaning they automatically lose their seat because working for the Crown is not seen as impartial.
Titles include the crown steward and bailiff of the Chiltern Hundreds and the Crown Steward and Bailiff of the Manor of Northstead.
Rachel Reeves has now appointed Amesbury to be steward and bailiff of the Three Hundreds of Chiltern, meaning the parliamentary seat is officially vacant.
Once he does, the chief whip will put forward a motion to Lindsay Hoyle, the Commons speaker, to officially begin the process of disqualifying the MP – known as “moving the writ”.
The Speaker then puts the motion to MPs for a vote. If they agree, the writ passes through the Commons and ends up with the returning officer in the local constituency who oversees the by-election.
The writ is typically issued within three months of the MP resigning from their seat and in doing so, the date of the by-election is fixed.
It could potentially coincide with the local elections in May.