Eurosceptic Conservatives refused to back a motion reiterating support for the prime minister’s negotiating strategy, deeply suspicious that she might try and use it to rule out a no-deal Brexit.
The loss brutally exposes how trust between Ms May and her backbenchers has hit rock bottom, with many still furious over comments made by her chief negotiator in a Brussels bar this week which also appeared to exclude a no-deal scenario.
But the defeat has also laid bare the extreme fragility of parliamentary support for her approach, with her ministers having claimed only last week that she had secured a “strong mandate” from the Commons.
On another dramatic night in parliament, Ms May was nowhere to be seen as the result was read out to cheers from the Labour benches. The government motion was defeated by 258 votes to 303.
One leading Tory described the night as a “fiasco”, Jeremy Corbyn said the country was heading for a “catastrophe”, and a senior source in Brussels said: “There goes the strong mandate.”
The Brexit fault line also cut through Mr Corbyn’s party on Thursday, with a significant number of Labour MPs apparently defying their leader’s will in a separate vote amid suspicions that some are close to breaking away.
But the spotlight was firmly on the prime minister’s ailing administration as it contorted in an attempt to avoid defeat on what did not have to be a difficult night for Ms May.
The wording of Thursday’s motion called on MPs to reiterate their support for the approach set out in an earlier set of votes on 29 January, when the Commons backed a plan to reopen negotiations with Brussels on the withdrawal agreement – but also voted for a non-binding amendment rejecting a no-deal Brexit.
After the government apparently combined support for both issues in Thursday’s motion, rather than just focussing on renegotiating with the EU, Tory Euroceptics who want to keep no deal on the table found themselves unable to back Ms May’s position.
It’s an unfortunate fiasco that the government’s clumsiness created
Conservative MP Bernard Jenkin
Government whips tried and failed in the hours running up to the vote to convince Brexiteers that backing the government on Thursday would not take no deal off the table.
After the defeat, prominent Eurosceptic Bernard Jenkin MP said: “It’s an unfortunate fiasco that the government’s clumsiness created.
“I don’t know why the government doesn’t consult a bit more widely before they table these motions. There are 110 Eurosceptic Tory MPs who helped defeat the withdrawal agreement – not one of us was consulted.”
The division list showed the government’s Brexit motion was supported by 243 of Ms May’s MPs. While just five of them voted against it, many Tories in the Brexit-backing European Research Group (ERG) abstained, robbing Ms May of her majority.
Steve Baker, vice-chair of the ERG, said its members were not prepared to be “coopted into taking no deal off the table”, but he insisted that Ms May retains “a clear mandate” from last month’s vote to negotiate a better deal with Brussels.
He said: “It’s time for some people to grow up and think about what is in the national interest. That is standing firm that we are leaving and then negotiating with the EU to get an acceptable deal.”
Mr Corbyn demanded the prime minister come back to the chamber with a “coherent plan” following the defeat, claiming the vote showed there is no majority for her course of action.
He went on: “The government cannot keep on ignoring parliament or ploughing on towards 29 March without a coherent plan.
“She can’t keep on just running down the clock and hoping that something will turn up that will save her day and save her face.”
A Downing Street spokesman accused Mr Corbyn of putting “partisan considerations” ahead of the national interest and voting in a way to make a no-deal scenario more likely.
He added: “While we didn’t secure the support of the Commons this evening, the prime minister continues to believe, and the debate itself indicated, that far from objecting to securing changes to the backstop that will allow us to leave with a deal, there was a concern from some Conservative colleagues about taking no deal off the table at this stage.
The spokesman said the government will now continue to seek legally binding changes to the withdrawal agreement in order to secure Britain’s departure from the EU on 29 March.
But the defeat does not bode well for a more significant set of votes coming on 27 February, when parliament could well use Commons amendments to take control of the process away from Ms May and delay Brexit.
Pro-Europe Tory Anna Soubry said: “This is a serious blow to the credibility of the prime minister. We are in such a mess, I’m afraid, that parliament is going to have to take back control of this.
“It is a symbol of the profound lack of leadership in both political parties.”
The Labour leader had ordered his MPs to abstain – but he was defied by 41 who voted with the Scottish Nationalists for a suspension of “no fewer than three months”, past 29 March.