Rebel Tory MPs are just eight votes short of forcing a leadership challenge that could oust Theresa May, it has been claimed.
As many as 40 Conservative backbenchers have signed letters saying they have no confidence in Mrs May's leadership, the Sunday Times reported.
It suggests that the Tories could be on the brink of a coup attempt against the Prime Minister, following two cabinet resignation in the past fortnight, an ongoing scandal over sexual harassment allegations, and continued deadlock in Brexit talks.
Meanwhile, a confidential letter has emerged in which Boris Johnson and Michael Gove appear to issue instructions to Mrs May on how to run Brexit preparations, underlining her weakness.
Transition arrangements for Britain's exit from the European Union must end on June 30 2021, the Cabinet ministers demanded, according to the Mail on Sunday.
They also urged the Prime Minister to ensure members of her top team fall behind their Brexit plans by "clarifying their minds" and called for them to "internalise the logic", the newspaper said.
The leaked letter appears to make a thinly veiled attack Chancellor Philip Hammond, who backed remain and wants a softer Brexit, for lacking the "sufficient energy" in preparing for the UK's future outside the bloc.
No 10 said it did not comment on leaks and neither Mr Johnson or Mr Gove commented.
Labour leader Jeremy Corbyn called for Mrs May to "govern or go" and demanded Mr Johnson to be sacked. In an article for The Sunday Times, he wrote: "Continuing uncertainty about the Government's approach to Brexit is now the biggest risk facing our country. The Prime Minister must end the confusion, take on the 'no-deal' extremists in her Government and back a jobs first Brexit for Britain."