Theresa May will fight any attempt to unseat her through a vote of no confidence by Conservative MPs, Downing Street said last night.
The defiant message came after Mrs May's administration was thrown into turmoil by the sensational resignations in quick succession of Brexit Secretary David Davis and Foreign Secretary Boris Johnson.
The departure of the two cabinet "big beasts" came just two days after Mrs May secured senior ministers' agreement at Chequers for a Brexit plan about which both men had expressed reservations.
As the Tory leader appeared at Westminster, she was greeted by loud cheers from Tory MPs and shouts of "resign" from the opposition benches.
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Conservative MP Andrea Jenkyns had earlier said she believed that Mrs May's time as prime minister was "over", telling BBC Radio 4 that she wanted a premier who would "provide true leadership and a positive post-Brexit vision for our country".
And senior backbencher Bernard Jenkin said there had been a "massive haemorrhage of trust" in Mrs May.
However, prominent Brexiteer Jacob Rees-Mogg, the chairman of the European Research Group of Eurosceptic backbenchers, said he had not submitted a letter of no confidence and expected Mrs May to remain at least until the official date of Brexit in March 2019.
To trigger a no-confidence vote in the prime minister, 15 per cent of Tory MPs must write to the chairman of the backbench 1922 Committee, currently Sir Graham Brady.
With 316 Conservative MPs in Westminster, Sir Graham must receive 48 letters to call a ballot.
If Theresa May chose to fight, she would need the support of more than 50 per cent of Conservative MPs – currently 159 – in the confidence vote to stay in office.
But even if she achieved that threshold, a narrow victory would seriously undermine her authority and may lead her to question whether it was worth carrying on.
If she lost the vote, she would not be able to stand in the subsequent leadership contest, arranged by the chairman of the '22.
Candidates for the leadership must be nominated by two Conservative MPs. If only one candidate comes forward, he or she becomes leader.
If a number of would-be leaders are nominated, the list is whittled down to a shortlist of two by MPs before being put to party members in the country.
In a series of secret ballots taking place within a few days at Westminster, MPs vote for their preferred leader, with the least popular candidate eliminated after each round until only two remain.
The final two then go to a postal ballot of all party members, with the position of leader, and Prime Minister, going to the victor.
Sir Graham would be responsible for overseeing the contest and setting a timetable for the campaign, which would be expected to last around 12 weeks.
Mrs May could remain in post during the campaign period.
