MPs have inflicted a major defeat on Theresa May by passing a motion that will drastically speed up the Brexit process.

The controversial move, known as the Grieve amendment, will force the prime minister to put forward an alternative plan within three days if her proposed withdrawal deal is voted down by the Commons next week.

Under current laws, she has three weeks to announce how she plans to proceed.

More than a dozen Tory MPs broke ranks to vote for the change, which was proposed by former attorney general Dominic Grieve and backed by other senior Conservatives.

It was passed by 308 votes to 297.

Opponents of a no-deal Brexit hope the move would make it harder for ministers to run down the clock and take Britain out of the EU with no agreement, unless they had secured parliament’s approval for such an outcome.

Currently Britain is on course to leave the bloc on 29 March regardless of whether ot not a deal is in place.

The move is not legally binding but is likely to pile pressure on Ms May to address parliament swiftly if her deal is rejected.

Mr Grieve’s amendment sparked a furious row, with Eurosceptic MPs accusing John Bercow, the Commons speaker, of acting unconstitutionally by allowing the vote to go ahead.

Under parliamentary rules, only a government minister can table a business motion outlining what the Commons will debate in the coming days. But to the fury of the government, Mr Bercow ruled that Mr Grieve’s motion was an amendment to the business motion and was therefore allowed.

He told MPs: “My understanding is the motion is amendable, I’m clear in my mind about that.”

“I’m trying to do the right thing and make the right judgments. That is what I have tried to do and what I will go on doing.”

Police separate clashing Brexit protesters outside Parliament Show all 11 1 /11 Police separate clashing Brexit protesters outside Parliament Police separate clashing Brexit protesters outside Parliament Anti-Brexit protester Steve Bray (left) and a pro-Brexit protester argue as they demonstrate outside the Houses of Parliament Getty Images Police separate clashing Brexit protesters outside Parliament A pro-Brexit protester argues Getty Images Police separate clashing Brexit protesters outside Parliament Police surround the pro-Brexit protester after he confronted Steve Bray, a pro-European protester Getty Images Police separate clashing Brexit protesters outside Parliament A leave supporter is spoken to by a police officer as he argues with a remain supporter, Steve Bray, outside Parliament PA Police separate clashing Brexit protesters outside Parliament MPs in Parliament are to vote on Theresa May's Brexit deal next week after her December vote was called off in the face of a major defeat Getty Images Police separate clashing Brexit protesters outside Parliament A leave supporter is spoken to by a police officer PA Police separate clashing Brexit protesters outside Parliament Police look on as anti-Brexit protesters demonstrate outside the Houses of Parliament. Getty Images Police separate clashing Brexit protesters outside Parliament Police hold back a leave supporter PA Police separate clashing Brexit protesters outside Parliament A police officer speaks with anti-Brexit protester Steve Bray Getty Images Police separate clashing Brexit protesters outside Parliament Police surround a pro-Brexit protester after he confronted a pro-European protester Getty Images Police separate clashing Brexit protesters outside Parliament Conservative MP David Davies, wearing a gopro camera, speaks to anti-Brexit protester Steve Bray Getty Images

But Tory MP Mark Francois, a leading Eurosceptic, said the decision was “ridiculous” and accused Mr Bercow of “utter sophistry”.

He said: “Mr Speaker, I have not been in this House as long as you but I have been here for 18 years and I have never known any occasion when any Speaker has overruled a motion of the House of Commons.

“You have said again and again you’re a servant of this House and we take you at your word, and I have heard you many times on points of order when people have challenged you say ‘I cannot do X or Y because I am bound by a motion of the House’.

“You have done that multiple times in my experience, so why are you overruling this today?”

Support free-thinking journalism and attend Independent events

In a heated exchange, Andrea Leadsom, the leader of the House, called on Mr Bercow to publish the advice he had received from parliamentary clerks. He refused, saying this was given “privately and that’s absolutely proper”.

The fresh defeat for Ms May came just hours after the government failed to block a motion that will make it harder for minister to implement a no-deal Brexit.