The Government has suffered another resignation as Tory Brexiteers ramp up the pressure on Theresa May to change her blueprint for leaving the European Union.
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".
On Monday night, MPs will consider amendments to trade legislation from Tory Eurosceptics 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.
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, 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.
It came as a former minister, Justine Greening, became the highest-profile Conservative MP to back the idea of a referendum on the terms of the UK’s Brexit deal.
Business Secretary Greg Clark pleaded with Jacob Rees-Mogg and his colleagues not to revolt over 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 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.
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.