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 EU withdrawal has said.

Former attorney general Dominic Grieve 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 Mrs May’s Government down.

He was speaking as Foreign Office minister Alistair Burt 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.”

Could any members of the PM's top team be prepared to quit? Credit: PA

Angry Tory loyalists have turned on the party’s Brexiteers after Mrs May’s plans suffered another humiliating Commons defeat on Valentine’s Day.

Business minister Richard Harrington 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.

Defence minister Tobias Ellwood accused the ERG of acting as “a party within a party” and described their behaviour as “provocative”.

Meanwhile, Margot James became the latest minister to rule out remaining in the Government if it allowed a no-deal Brexit.

The Digital Minister told Channel 4 News: “I could not be part of a government that allowed this country to leave the European Union without a deal.”

Tobias Ellwood has accused the ERG of operating as a ‘party within a party’ Credit: PA

Downing Street insisted the Prime Minister would continue with her negotiating strategy, with ministers dismissing Thursday’s vote as no more than a “hiccup”.

Number 10 said Mrs May spoke to the Polish President Mateusz Morawiecki, the Estonian Prime Minister Juri Ratas and the Lithuanian President Dalia Grybauskaite on Friday afternoon.

Leader of the Commons Andrea Leadsom 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.”

Ms 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 fell to 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.

It starts to bring into question whether in fact the Government is able to operate in the national interest at all Dominic Grieve

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, Mr Grieve said: “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.”

ERG deputy chairman Steve Baker dismissed the row over Thursday’s vote as a “storm in a teacup”.

Steve Baker has dismissed the furore over the ERG as a ‘storm in a teacup’ Credit: Dominic Lipinski/PA

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 said.

He 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.

“I’m afraid people didn’t want to be treated like that twice,” Mr Baker told Today.

“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.”

Credit: PA Graphics

Greek foreign minister George Katrougalos told Today that Thursday’s vote was “part of the contradictory message that we are receiving as the 27 from the UK”.

Mr Katrougalos 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.”

It was “not foreseeable” that the EU would reopen negotiations or take the backstop out of the UK’s Withdrawal Agreement, he said.