A dozen or more Government ministers could quit by the end of the month if Theresa May refuses to extend the Brexit negotiating period beyond March 29, a leading Tory opponent of Britain’s withdrawal from the EU has suggested.

Dominic Grieve, the former Attorney General, said that the next round of Brexit votes on February 27 would be a "High Noon" moment when resignations on this scale - which he said could include six Cabinet members - might bring the Prime Minister’s Government down.

He was speaking as Alistair Burt, the Foreign Office Minister, made clear his unwillingness to accept a no-deal departure, telling hardline Brexiteers in a tweet: "We are not leaving without a deal. If you want to leave, you'd better agree one. In the next fortnight would help."

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The Herald reported that a Cabinet Minister has suggested Mrs May will come forward with a “form of words” to reassure colleagues that the Government would not allow a no-deal departure before the next Commons vote, due on February 27, which the minister described as the “moment of truth”.

Asked if the PM believed she had to secure concessions from Brussels before that vote, her deputy spokeswoman replied: “We are looking for changes to the backstop, to deliver those as soon as possible so we can bring the meaningful vote back.”

Asked if as soon as possible meant before February 27, she replied: “It’s as soon as possible.”

The deputy spokeswoman was also questioned about whether Mrs May believed she could keep her Cabinet intact after the February 27 vote and said this was based on a hypothetical, stressing: “The PM is focused on securing changes to the backstop so a deal can be passed.”

Next week, Mrs May is expected to travel to Brussels for another meeting with Jean-Claude Juncker, the European Commission President, as Stephen Barclay, the Brexit Secretary, and Geoffrey Cox, the Attorney General, also travel to the Belgian capital for talks with senior EU officials.

Today, Mr Barclay will meet the UK-based ambassadors of the EU27 while Mrs May is expected to continue her range of phonecalls with European leaders; she has already spoken to several, including Germany’s Angela Merkel and France’s Emmanuel Macron.

Downing St knocked back suggestions that the Brexit Secretary in talks with Michel Barnier, the EU’s chief negotiator, had conceded that Brussels did not have to reopen the Withdrawal Agreement to enable the UK to get legal assurances on the backstop.

The PM’s deputy spokeswoman made clear that Mrs May continued to seek a reopening of the initial deal to get the “legally binding changes” to address the concerns of MPs on the backstop.

Asked if that would involve reopening the Withdrawal Agreement, she replied: “That is what the PM has said, yes.”

The deputy spokeswoman also rejected suggestions that the Commons defeat on Thursday evening had undermined the Government’s Brexit strategy, stressing how the one and “only” vote, which expressed the will of Parliament on January 29, reflected a clear determination to change the backstop and that was what Mrs May was vigorously pursuing.

Following yet another Commons defeat for the PM, angry Tory loyalists have turned on the party's Brexiteers.

Richard Harrington, the UK Business Minister, accused the European Research Group [ERG], led by Jacob Rees-Mogg, of "treachery" and said they were "not Conservatives" and should join former Ukip leader Nigel Farage's new Brexit Party.

His colleague Tobias Ellwood, the Defence Minister, accused the ERG of acting as "a party within a party" and described their behaviour as "provocative".

Downing St made clear the PM would continue with her negotiating strategy with ministers dismissing Thursday's vote as no more than a "hiccup".

Andrea Leadsom, the Commons Leader, acknowledged that Thursday's defeat had not strengthened Mrs May's hand in her effort to persuade the EU to change the proposed backstop arrangements to keep the Irish border open after Brexit.

But she told BBC Radio 4's Today programme: "The Prime Minister carries on. She will continue to seek those legally binding changes to the backstop that will enable Parliament to support our deal.

"The one problem with last night's vote is that it allows the EU to continue with this pretence that they don't know what we want. They do know what we want."

Mrs Leadsom did not discount the possibility of ministerial-level resignations, telling Today: "Resignations from government do happen...People have very, very strong, heartfelt views about leaving the EU or remaining within it. That is a matter for them as individuals."

But she insisted: "The vote yesterday didn't change anything. The Government's position remains to resolve the issues of the backstop and then come back to Parliament with a fresh meaningful vote. It's essential we crack on with that work, and that's what we are doing."

There was fury among some Conservative MPs after an announcement by the pro-Brexit ERG moments before the crucial vote on Thursday evening that its members had taken a "collective decision" to abstain.

With some Remainers also failing to vote, and five Tory MPs voting with the opposition, the Government suffered a 303 to 258 vote defeat.

Mr Grieve said the ERG "seem to be completely cavalier about the risks that the country might run if we leave with no deal", something which he said the "overwhelming" majority of MPs were not prepared to accept.

He told Today that he understood a number of ministers had already told Mrs May that if she was unable to secure a Withdrawal Agreement which could command the support of the Commons, she should extend the two-year Article 50 negotiating period.

If she refused, he said "a dozen or even more" ministers may resign, including "up to half a dozen" from the Cabinet.

Asked whether this could bring down the Government, the Buckinghamshire MP replied: "Yes, it could and this isn't a desirable outcome.

"The irony of all this is that most of us in the Conservative Party are sufficiently united to want to try to operate a coherent Government. But the truth is we're finding it harder and harder to do.

"It starts to bring into question whether in fact the Government is able to operate in the national interest at all. We are facing a great crisis and we are not really looking at all the options for trying to resolve it," he added.

But Steve Baker, the ERG Deputy Chairman, dismissed the row over Thursday's vote as a "storm in a teacup".

Brexit-backing MPs who abstained were not prepared to be associated with the "catastrophic and foolish negotiating error" of taking a no-deal Brexit off the table, he explained.

The former Brexit Minister accused Mrs May of "reinterpreting" last month's vote, which authorised her to replace the backstop with alternative arrangements to avoid a hard border in Ireland”.

He insisted: "I'm afraid people didn't want to be treated like that twice. I really do rather object to being called 'hardline' when what we are doing is trying to deliver an exit with a deal which works for everybody, with a transition period. We are making enormous compromises to work across the party."

Meanwhile, George Katrougalos, the Greek Foreign Minister, complained that Thursday's vote was "part of the contradictory message that we are receiving as the 27 from the UK".

He said: "It complicates even further the situation. It's very, very difficult to be optimistic about Brexit under these circumstances. I cannot exclude a miracle. Miracles happen but I cannot see what kind of miracle it is that could save the day."

Mr Katrougalos said it was "not foreseeable" that the EU would reopen negotiations or take the backstop out of the UK's Withdrawal Agreement.