A secret letter from Boris Johnson and Michael Gove giving Theresa May apparent instructions on how to run Brexit has emerged.
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 British 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 on 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.
A senior British Government source told the newspaper the UK's Foreign Secretary and Environment Secretary had conducted a "soft coup" and described Mrs May as "their Downing Street hostage".
It comes as The Sunday Times reported that 40 Tory MPs had agreed to sign a letter of no confidence in Mrs May - eight short of the number needed.
The leaked letter to the PM from Mr Johnson and Mr Gove, titled EU Exit - Next Steps, is marked "For your and Gavin's eyes only", a reference to the PM's chief of staff Gavin Barwell.
It states: "Your approach is governed by sensible pragmatism. That does not in any way dilute our ambition to be a fully independent self-governing country by the time of the next election. If we are to counter those who wish to frustrate that end, there are ways of underlining your resolve.
"We are profoundly worried that in some parts of Government the current preparations are not proceeding with anything like sufficient energy.
"We have heard it argued by some that we cannot start preparations on the basis of 'No Deal' because that would undermine our obligation of 'sincere co-operation' with the EU. If taken seriously, that would leave us over a barrel in 2021.
"We all want you to push your agenda forward with confidence and have your Government articulate the following..."
No 10 said it did not comment on leaks and neither Mr Johnson or Mr Gove commented.
Labour leader Jeremy Corbyn, meanwhile, called for Mrs May to "govern or go" and demanded Mr Johnson to be sacked for "undermining our country" and "putting our citizens at risk".
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."
In a statement to the Observer, he wrote: "We've put up with Johnson embarrassing and undermining our country with his incompetence and colonial throwback views and putting our citizens at risk for long enough. It's time for him to go."