John Bercow has announced that he will stand down as Commons Speaker at the next election or by the 31st October at the latest.
Speaking in Parliament, an emotional Mr Bercow said his "tenure" was nearing its end and it had been the "greatest honour and privilege" to serve as Speaker for ten years.
He said if there was no early election, the 31 October would be the "least disruptive and most democratic" date to step down.
He was applauded by opposition MPs, but only a handful from the Tory side.
The ex-Tory Buckingham MP has faced fierce criticism from Brexiteers, who have questioned his impartiality on the issue of Europe.
They also claim he has facilitated efforts by MPs opposed to a no-deal Brexit to take control of Commons business.
Bercow succeeded the late Michael Martin as Speaker in 2009.
Watched by his wife Sally in the gallery, he said: "I wish my successor the very best fortune in standing up for the rights of MPs individually and for parliament institutionally."
Who is likely to be the next Speaker?
Sir Lindsay Hoyle is the odds-on favourite for the role, according to betting agency Ladbrokes.
The Commons’ most senior deputy speaker is widely thought to be running.
He said earlier this year: “When the Speaker decides to go, I may well enter that race. But I’ll certainly wait for the starting gun first.”
The Labour MP for Chorley is said to be a popular figure in Westminster.
Sir Hoyle is priced at 4/6, followed by Harriet Harman at 5/1, Rosie Winterton at 8/1 and Chris Bryant at 9/1.
How is the Speaker selected?
The Speaker is elected by a secret ballot of MPs at the beginning of a new Parliament, following a general election, or following the resignation, death or retirement of the previous speaker.
MPs are given a list of candidates and place an “x” next to the candidate of their choice.
If a candidate receives more than 50 per cent of the votes, the question is put to the House that he or she takes the chair as Speaker.
If the Speaker in post wishes to retain the role following a general election, they do not need to be re-elected by secret ballot and can instead be reappointed by a motion passed by a majority of MPs.
What does the speaker actually do?
The Speaker is the chief officer and highest authority of the House of Commons and must remain politically impartial at all times.
He/she represents the Commons to the monarch, the Lords and other authorities and chairs the House of Commons Commission.
But the Speaker is perhaps best known as the person who keeps order and calls MPs to speak during Commons debates.
He/she calls MPs in turn to give their opinion on an issues and directs an MP to withdraw remarks if, for example, they use abusive language.
The speaker can suspend the sitting of the House due to serious disorder.
What has been the reaction to Bercow’s resignation?
Labour leader Jeremy Corbyn thanked Mr Bercow for his "superb" record, adding: "Our democracy is the stronger for your being the speaker."
"As somebody who aspires to hold executive office, I like the idea of a powerful parliament holding the executive to account.
"It's something I've spent the last 35 years doing myself."
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Michael Gove, a long-serving cabinet minister and chancellor of the Duchy of Lancaster, paid tribute to Mr Bercow's "unwavering" commitment to his principles and constituents.
"Your role as the backbenchers' backstop is certainly one that has been appreciated by individuals across this house,"