Tory infighting over Europe has intensified after leading Brexiteer Jacob Rees-Mogg told Theresa May she must deliver what she promised or risk the collapse of her Government.
The Prime Minister will face MPs on Monday afternoon ahead of a crunch meeting of her Cabinet at Chequers on Friday to thrash out the Government's plans for the future relationship with Brussels.
Downing Street was reportedly preparing to discuss a third customs model for post-Brexit trade with the Cabinet in a bid to overcome disagreement on the issue.
Meanwhile, Mrs May faces repeated warnings that senior figures in her government are on manoeuvres in preparation for a leadership battle.
Mr Rees-Mogg, tipped as a potential Tory leader, insisted he was "confident" that Mrs May would deliver the Brexit she had promised - with the UK leaving the single market and customs union and outside the jurisdiction of the European Court of Justice.
But writing in The Daily Telegraph, Mr Rees-Mogg warned the PM that backsliding could result in splitting the party like Sir Robert Peel, who plunged it into the political wilderness for nearly three decades following bitter divisions over trade reforms.
The chairman of the European Research Group of Brexit-backing Tories said: "Theresa May must stand firm for what she herself has promised.
"One former Tory leader, Sir Robert Peel, decided to break his manifesto pledge and passed legislation with the majority of his party voting the other way.
"This left the Conservatives out of office for 28 years.
"At least he did so for a policy that works. At Chequers (Mrs May) must stick to her righteous cause and deliver what she has said she would, she must use her undoubted grace to persevere."
Mr Rees-Mogg's intervention prompted a furious backlash from Remain-voting Tories.
Foreign Office minister Sir Alan Duncan accused him of "insolence", claiming his comments risked "debasing" the Government, Tory Party and the country as a whole.
"The ideological right are a minority despite their noise and should pipe down," he added.
North Dorset MP Simon Hoare said "the hectoring nonsense" and "blackmail" had to stop.
The Conservatives had to wake up to the reality of the parliamentary arithmetic and the potential "calamity" of a Jeremy Corbyn-led government, he added.
Tory MP Vicky Ford - a former MEP and supporter of close ties to Europe - told BBC Radio 4's Today programme: "What I would say to Jacob ... is if this becomes a binary choice between staying in the single market and customs union or no deal, then I do not believe there is a majority for no deal."
But former Conservative leader and Brexiteer Lord Howard told Today: "The Prime Minister has made a series of promises, the Prime Minister has repeatedly said that we must regain control of our laws, our money and our borders.
"I have great confidence in the Prime Minister. I am sure that she will deliver a Brexit that is entirely consistent with the promises she has made."
The row comes after the PM's chief Brexit official reportedly told ministers they have no chance of striking a bespoke trade deal with Brussels.
Briefing Cabinet ministers ahead of the Chequers talks, Oliver Robbins is said to have painted a bleak picture of the situation, with a source telling The Times they came out of the meeting thinking "we were even more screwed than we were before".
Business Secretary Greg Clark and Commons Leader Andrea Leadsom both refused to rule out an extension to transition arrangements in the face of demands from Tory backbenchers for the timetable to be maintained.
Mr Clark said the decision must be "guided by the facts and the evidence" and Mrs Leadsom said December 2020 was not a "magical date".
Mrs May will bring together her Cabinet at her country residence to thrash out details of a white paper setting out the UK's plans for areas such as trade.
Brexiteers oppose the PM's favoured option of a customs partnership with the EU, which would see the UK collect tariffs set by the EU customs union on goods entering the country on behalf of the bloc.
Their "max fac" alternative would, rather than scrapping customs checks, use technology to minimise the need for them.
Both options have been dismissed by the EU.
According to the BBC, No 10 has produced a third model for handling customs after Brexit which will be discussed by senior ministers at the gathering on Friday.