Theresa May vowed defiance after Brexiteers effectively declared war - with Cabinet ministers quitting and an all-out bid to oust her.
The Prime Minister is fighting for her political life - and used a press conference in Downing Street to double down on her determination to press ahead with her controversial pact with the EU.
Despite a slew of high-profile resignations and the near-certain prospect of a Tory no-confidence vote in her leadership, May insisted she would keep "putting the national interest first".
"I believe with every fibre in my body that the course I have set out is the right one," she said.
She admitted that the burden of leadership was "heavy\" at the best of times and even tougher when Brexit pervaded every part of the UK economically and socially.
Asked if she would fight on even if she only wins a Tory no-confidence ballot by one vote, May retorted: "Am I going to see this through? Yes."
The Prime Minister is braced for a Tory no-confidence vote to be triggered after she vowed to push on with her controversial Brexit plan despite Dominic Raab and Esther McVey quitting accusing her of bowing to EU "blackmail".
Other junior ministers have also resigned as the situation threatens to spiral out of control, with the Pound plunging as markets take fright at the chances of a Brexit deal receding. In a dramatic twist, there are claims Michael Gove has turned down the chance to take over as Brexit Secretary, saying he would want to renegotiate the whole package with the EU.
May has called a press conference for 5pm (UK time) as she bids to get a grip on the civil war raging in her party - amid speculation she could herself call a ballot of Conservative MPs and demand critics 'put up or shut up'.
In devastating exchanges in the Commons minutes after the bombshells dropped, the premier was mauled by MPs from all sides over her 'dogs dinner' package.
And Tory Eurosceptic Jacob Rees-Mogg signalled an all-out assault by demanding she tell him why he should not write to the powerful Tory 1922 committee urging a no-confidence vote.
At a meeting of the powerful Conservative ERG block this afternoon also attended by Boris Johnson, Rees-Mogg confirmed that he had put in his letter, saying May had 'failed to meet her promises' and it was 'too late' for her to turn it around.
And at a press conference afterwards he denying mounting a 'coup' but said: 'This is not Brexit. This is a failure of government policy.'
The hardline Brexiteer ruled out running in any leadership contest - picking out Boris Johnson, Dominic Raab, David Davis and Penny Mordaunt as contenders.
MailOnline has learned government whips are now canvassing MPs on which way they will vote - suggesting they believe the trigger threshold of 48 letters has been reached. Downing Street insisted she will fight if a challenge is held. If she does not secure backing from a majority of MPs a full leadership contest would be triggered.
A party vote of no confidence would take a matter of days. But if May loses, a leadership contest could take months - although some MPs claim it can be done in as little as two weeks.
Despite Brexiteer and Remainer MPs from across parties lining up to condemn her plans in the Commons, the PM defiantly pledged she would carry on in the "national interest" even if the compromises involved were not "comfortable".
"I will bring it to Parliament and ask MPs to consider it in the national interest," she said.
"The choice is clear. We can choose to leave with no deal. We can have no Brexit at all. Or we can choose to unite and support the best deal that can be negotiated.
"I choose to deliver for the British people. I choose to do what is in the national interest."
But barely any MPs spoke up for May's position - further fuelling fears of a fatal threat to her leadership.
In signs of increasing desperation, there are claims that Mrs May offered Michael Gove the Brexit Secretary job in a bid to stop him walking out - but he turned it down.
Despite ERG head Rees-Mogg, former minister Steve Baker and backbencher Henry Smith confirming their letters had gone in, other senior figures said there was still a "difference of opinion" over whether May should be challenged.
Veteran Brexiteer Sir Edward Leigh said: 'If you succeed in this coup detat you just strengthen her opinion. There is also the question of loyalty. The problem is intractable.
"I believe we should stop this deal by voting it down in Parliament."
In interviews today, Raab played down calls for a change in the leadership saying he had "respect" for May and "supports this Prime Minister".
"I remain loyal to this Prime Minister, I want her to stay in office," he told Sky News.
Raab is understood to have endorsed the draft deal "with a heavy heart" at a fraught five-hour Cabinet meeting yesterday, but harboured deep concerns about the UK being locked into the Irish border "backstop".
In his resignation letter, Raab - who only succeeded David Davis in the post in July - said he had "enduring respect" for May but added: "I cannot in good conscience support the terms proposed for our deal with the EU."
McVey, who made what was described as an "emotional" assault on the Brexit deal during Cabinet yesterday, said in her letter that it did not "honour the result of the referendum".
"Indeed it doesn't meet the tests you set from the outset of your premiership," she added.
The resignations came in quick succession after Northern Ireland minister Shailesh Vara announced his departure, this morning claiming May is trying to "shackle" Britain to the EU "indefinitely".
Brexit minister Suella Braverman has quit, as has ministerial aide Anne-Marie Trevelyan - a strong supporter of Boris Johnson.
Aid Secretary Penny Mordaunt is also believed to be on the edge. She was in the Commons chamber this morning answering questions on her brief.
Fevered speculation erupted after Gove cancelled a visit in Yorkshire, although aides insisted it was for personal reasons. They did not respond to questions about whether he was quitting.
As rumours swept Westminster today, there are claims Mr Gove has been offered the Brexit Secretary job but is insisting he should be able to renegotiate the deal with the EU.
Remainer Tory MP Anna Soubry said Raab's resignation "marks the end of PMs Withdrawal Agreement" and called for a "government of national unity".
The mounting crisis is on the verge of torpedoing the entire package painstakingly thrashed out with Brussels over two years - and throwing May herself out of power.
EU council leader Donald Tusk nodded to the problems this morning as he said a summit to sign off the deal will happen on November 25 "if nothing extraordinary happens".
In a pointed aside later, he told reporters later: "The EU is prepared for a final deal with the United Kingdom in November," he told a news conference in Brussels.
"We are also prepared for a no-deal scenario but of course we are best prepared for a no-Brexit scenario."
In his resignation letter, Raab said: "I regret to say that, following the Cabinet meeting yesterday on the Brexit deal, I must resign.
"I understand why you have chosen to pursue the deal with the EU on the terms proposed, and I respect the different views held in good faith by all of our colleagues.
"For my part, I cannot support the proposed deal for two reasons. First, I believe that the regulatory regime proposed for Northern Ireland presents a very real threat to the integrity of the United Kingdom.
"Second, I cannot support an indefinite backstop arrangement, where the EU holds a veto over our ability to exit.
"The terms of the backstop amount to a hybrid of the EU Customs Union and Single Market obligations.
"No democratic nation has ever signed up to be bound by such an extensive regime, imposed externally without any democratic control over the laws to be applied, nor the ability to decide to exit the arrangement.
"That arrangement is no also taken as the starting point for negotiating the Future Economic partnership.
"If we accept that, it will severely prejudice the second phase of negotiations against the UK."
Vara said the draft agreement "leaves the UK in a halfway house with no time limit on when we will finally be a sovereign nation".
In an eviscerating resignation letter he added: "We are a proud nation and it is a sad day when we are reduced to obeying rules made by other countries who have shown that they do not have our best interests at heart. We must and can do better than this."
May acknowledged last night that she has "difficult days" ahead with Brexiteers in her party openly plotting to topple her - while warning: "It is this or Jeremy Corbyn."