THERESA May’s Brexit deal was all but killed off in the Commons last night, as MPs inflicted another humiliating defeat on the Prime Minister.

The Tory chief responded by publicly abandoning her authority as party leader, telling her ministers and MPs that they could do what they want in a vote being held tonight on ruling out a no-deal Brexit.

It was another remarkable day in Parliament. In January, May’s deal was rejected by a margin 230 votes, the biggest defeat of any UK government in history. Yesterday’s defeat, by 391 MPs to 242, a margin of 149, was the fourth biggest defeat of any UK government in history.

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Assurances that the deal had changed, that Brussels had conceded ground on the backstop and its permanence, won over 40 of the 118 hardliner backbenchers who voted against it last time, including Scottish Tory John Lamont.

But defeat was all but guaranteed earlier in the afternoon when the DUP and the European Research Group of Tory backbenchers announced plans to reject the deal.

Their problem with the new package negotiated by May, and described by her as legally binding, was it would not remove the risk that the UK could be kept in the backstop, it would only “reduce” the risk.

“It didn’t deliver on the commitment to leave the EU cleanly,” Jacob Rees Mogg told the BBC.

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Speaking to the Commons after the defeat, May confirmed that MPs were to get a vote on ruling out a no-deal Brexit tonight, followed by a vote on extending article 50 tomorrow, if no deal is rejected.

The Prime Minister, who famously and repeatedly said that no deal was better than a bad deal, told MPs that she could now not support no deal herself.

“I have personally struggled with this choice as I am sure many other honourable members will.

“I am passionate about delivering the result of the referendum. But I am equally passionately believe that the best way to do that is to leave in an orderly way with a deal and I still believe there is a majority in the house for that course of action.

“And I am conscious also of my duties as Prime Minister of the United Kingdom of Great Britain and Northern Ireland and of the potential damage to the Union that leaving without a deal could do when one part of our country is without devolved governance.”

Today’s vote will not take no deal off the table entirely, but allow Parliament to say it should not happen on 29 March.

May also promised to “publish information on essential policies which would need to be put in place if we were to leave without a deal.”

These are expected today, and will cover tariffs and the Northern Ireland border.

She added: “Voting against leaving without a deal and for extension does not solve the problems we face. The EU will want to know what use we mean to make of such an extension and this house will have to answer that question.

“Does it wish to revoke article 50, does it want hold a second referendum, or does it want to leave with a deal but not this deal?”

Labour leader Jeremy Corbyn, raising a point of order, called for a general election: “The Government has been defeated again by an enormous majority. They must now accept their deal is clearly dead and does not have the support of this House. Quite clearly, no-deal must be taken off the table.”

In a statement after the vote, Nicola Sturgeon said the chaos in Westminster was proof that “a handful of DUP MPs” have “more sway over Scotland’s future than our own national Parliament”.

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A spokesman for European Council president Donald Tusk said Brussels regretted the outcome: “On the EU side we have done all that is possible to reach an agreement. Given the additional assurances provided by the EU in December, January and yesterday, it is difficult to see what more we can do.

“If there is a solution to the current impasse, it can only be found in London,” he added.

Tusk’s spokesman warned the result “significantly increased the likelihood of a no-deal Brexit”.

“We will continue our no-deal preparations and ensure we will be ready if such a scenario arises,” he said.

Tory MP Steve Double, who admitted he was unsure how to vote, made the most memorable contribution to the debate, describing May’s agreement as a “turd of a deal, which has now been taken away and polished so that it is a polished turd”, but, he conceded, “it might be the best turd that we have before us”.