Theresa May is under intense pressure from Tory Brexiteers to change her controversial blueprint for leaving the European Union.

Cabinet minister Greg Clark pleaded with Tory Eurosceptics who have tabled amendments to the Government’s customs bill aimed at imposing strict conditions on the Prime Minister after she produced a plan which would keep the UK closely tied to Brussels’ rules on goods and food.

The amendments could be used as a show of strength by the Brexiteers, who are furious at the Chequers plan, but there were signs at Westminster that Mrs May could be prepared to compromise in an effort to avert a damaging blow to her authority.

Jacob Rees-Mogg, leader of the pro-<a href=Brexit European Research Group of Tories (Stefan Rousseau/PA)">Jacob Rees-Mogg, leader of the pro-Brexit European Research Group of Tories (Stefan Rousseau/PA)

A senior Government source said “no decision yet” had been made on whether to accept the amendments supported by arch-Eurosceptics including Jacob Rees-Mogg, Sir Bernard Jenkin, Priti Patel and Iain Duncan Smith.

A Brexiteer source said that while ministers “haven’t yet” accepted the amendments “all the noise is in that direction”.

Business Secretary Mr Clark was challenged about the potential revolt on the Taxation (Cross-border Trade) Bill, often referred to as the customs bill.

On BBC Radio 4’s Today programme he urged Tory colleagues who “want to get on with Brexit” to acknowledge that the Bill was “essential” and should not be impeded.

Asked if there was a suggestion that ministers would accept the amendments he said: “No. The Bill is an important part of preparing for the world after Brexit and I would have thought that all colleagues would respect the fact that we need to get those preparations in place whilst having this important negotiation to make sure that our trading arrangement can continue to support prosperity in the future.”

Sir Bernard told the programme that the Chequers plan was “dead”, with opposition from both wings of the Tory party.

“I’m afraid it is neither beloved by Remainers or Leavers.

“It’s also quite likely to be either rejected by the EU or more demands will be made upon it so it will be even less acceptable.”

Mr Rees-Mogg, the leader of the pro-Brexit European Research Group (ERG), played down suggestions over the weekend they were seeking to topple Mrs May, saying she still had time to change course on her proposals.

However, the danger to the Prime Minister was underlined by the disclosure that Brexiteers had set up a WhatsApp group to co-ordinate voting tactics, organised by ex-Brexit minister Steve Baker, who quit over the Chequers plan.

The Daily Telegraph reported more than 100 MPs had joined the group, more than double the 48 needed to submit letters of no confidence in the Prime Minister to force a leadership contest.

North Cornwall MP Scott Mann quit as a ministerial aide to the Treasury, the former postman saying he would not “deliver a watered down Brexit”.

The threat from the Brexiteers is not the only danger facing Mrs May, with pro-EU Tories tabling amendments of their own to the customs bill and the Trade Bill, which returns to the Commons on Tuesday, which would keep Britain in a customs union with the EU.

BrexitFormer education secretary Justine Greening has called for a second referendum (Stefan Rousseau/PA)

It was unclear whether they will actually press them to a vote after some pro-EU MPs backed Mrs May’s Chequers plan and EU white paper.

However, in a sign of just how volatile the party has become, former education secretary Justine Greening, who backed Remain, denounced the plan, saying it offered the “worst of both worlds” and called for a second referendum.

“The only solution is to take the final Brexit decision out of the hands of deadlocked politicians, away from the backroom deals, and give it back to the people,” she said in an article for The Times.

Meanwhile Boris Johnson, in his first public intervention since his resignation last week, appealed for people to take a more positive view of Britain’s prospects outside the EU.

In a sign that he was keeping his powder dry, he said in an article for The Daily Telegraph that he would resist “for now” the temptation “to bang on about Brexit”.

“It is time for all of us, at this critical moment in our constitutional development, to believe in ourselves, to believe in the British people and what they can do, and in our democracy,” he wrote.

“People around the world believe passionately in Britain. It’s time we shared their confidence.”