Prime Minister Theresa May suffered a heavy Brexit defeat on Tuesday, casting into doubt Britain's prospects of leaving the EU. In a personal blow to the embattled leader, MPs rejected her deal by 391 votes to 242 after 24 hours of frantic diplomacy and a wildly fluctuating pound. An earlier version of the plan was defeated by the largest margin in parliamentary history. Hopes of a deal rose overnight after a last-ditch mission to Strasbourg by Mrs May to secure concessions that she hoped would avert a second heavy defeat in two months. But the prospects of getting her deal through were effectively crushed on Tuesday morning when Attorney General Geoffrey Cox failed to convince critics that Mrs May had secured enough changes to the plan that was crushed by 230 votes in January. After the second defeat, by 149 votes, Mrs May told MPs: "I profoundly regret the decision that this House has taken tonight." The defeat on Tuesday clears the way for further votes in Parliament on Wednesday that could clear the way for a "no-deal" Brexit, which would end decades of European integration on March 29, or allow MPs to request a delay. Mrs May said all Conservative MPs would be allowed a free vote on the no-deal Brexit and aides said that she would personally vote against the possibility of crashing out without an agreement. She said that if the Commons declined to vote for a no-deal Brexit on Wednesday, a vote to extend Article 50, the legal mechanism removing the UK from the EU on March 29, would take place on Thursday. Mrs May and her ministers repeatedly warned before Tuesday’s vote that defeat could lead to opponents of Brexit taking control of the process and pushing for a second referendum. “If this vote is not passed tonight, if this deal is not passed, then Brexit could be lost," she told MPs during a debate on her plan on Tuesday. It is also likely to increase pressure on Mrs May, who faced calls from members of her own party to quit or call a general election to break the impasse. But British media has reported that the Prime Minister has not discussed resignation with her Cabinet yet. “The government has been defeated again by an enormous majority,” opposition leader Jeremy Corbyn said. “The deal the Prime Minister has put forward is clearly dead and does not have the support of this house. "No deal must be taken off the table. We’ve said it before and I’ll say it again.” Mr Corbyn then called for a general election, but did not mention the prospect of a second referendum. The scale of the defeat means there is no way of knowing how, or even if, Britain will leave the world’s largest trading bloc this month. Boris Johnson, the former Foreign Secretary who quit over Mrs May’s tactics, said the premier’s plan had “reached the end of the road”. “I would hope it will be put to bed and we can all face up to the reality of the position and the opportunity that we have,” Mr Johnson told MPs before the vote. Optimism that Mrs May could have finally found a way to persuade her wavering allies to back the deal came late on Monday after a meeting with Jean-Claude Juncker, the president of the European Commission. Some MPs who voted against the deal in the first vote came out to back it but most opponents said their views had not changed after Mr Cox's intervention. He said there remained a “legal risk” that Britain could indefinitely remain in a "backstop", designed to prevent a hard border on Ireland. Brexiteers, including those among Conservatives, are vehemently against any sort of deal that could lead to the UK staying tied to the EU indefinitely. Mr Johnson described it as “being trapped in the prison of the backstop”. A Eurosceptic arm of the Conservative party known as the European Research Group, whose support the government desperately needs, said the deal was not good enough. The pound fell sharply from recent highs plunging more than one per cent on the day against the euro. Labour's shadow Brexit secretary, Sir Keir Starmer, said the government's plans were in tatters. Charles Walker, a Conservative MP, said that a general election was now the way out of the impasse.<br/> A government minister said the outcome was dreadful and warned the Conservative Party could split. “We are in a very difficult position,” he said. The UK held a referendum in 2016, in which a 51.9 per cent of voters chose to leave the world's largest trading bloc.