Conor Burns, Johnson’s former Parliamentary aide, issued what appeared to be a veiled threat saying the PM could “change” if she didn’t budge on the policy.
Fellow MP and Boris ally Ross Thomson said May’s EU exit proposals were like being “shackled to a corpse”, adding that the party would lose key marginals like Mansfield if it went ahead.
Lead backbench Brexiteer Jacob Rees-Mogg called for a “red-blooded, Conservative approach”. The Chequers plan was now “not only a dead duck in a thunderstorm, it is the deadest of dying ducks”, he said.
Amid growing unease among both ‘Remain’ and ‘Leave’ wings, Tory splits over Europe threatened to turn into full-blown civil war at the party’s conference in Birmingham.
Burns even suggested that fellow MP and pro-EU rebel Sarah Wollaston could be replaced by a young Brexiteer, a claim he later said was “a joke”.
Former Attorney General Dominic Grieve said if May refused to rule out at second referendum she could be toppled from power.
A packed conference fringe, attended by several hundred activists and hosted by the BrexitCentral campaign group on Sunday evening, saw standing ovations for Rees-Mogg, Thompson and Burns.
May has defiantly defended her ‘Chequers’ plans, which include a common set of rules between the EU and UK in future trade links, despite fears that up to 40 MPs could vote against the proposals this autumn.
Burns, who quit as a Parliamentary Private Secretary in protest over the PM’s approach, said: “If Chequers had a slogan, it would be ‘not in Europe, but run by Europe’.”
“I say this in a spirit of friendship and affection towards our Prime Minister, Prime Minister, we don’t want to change you, we want to change the policy of Chequers. Please, please.”
His remarks were swiftly interpreted as a veiled threat to May that if she went ahead with her plans she would be defeated, a prospect that some MPs want to use to trigger a leadership challenge.
Burns heaped praise on Darren Grimes, a student Vote Leave campaigner at the centre of a probe into alleged misspending during the 2016 referendum, declaring he had been “victimised and persecuted by the provisional wing of Remain”.
He said that Grimes was so impressive that he should be a Parliamentary candidate, then referred to Wollaston’s constituency. “Have a good look down in Totnes. You’d be brilliant,” he said, to cheers.
But the most withering attack on the PM came from Thomson, MP for Aberdeen South, who said that Chequers had ‘humiliated’ the UK on the international stage.
“Chequers is an unmitigated disaster, it has humiliated us at home and in the EU and it is breaking this party apart.”
He added that the ‘Opportunity’ slogan of the 2018 Tory conference was missing some key words: “I couldn’t help but think [they were] ‘missed’, ’lost, ‘wasted’ and ‘squandered’.”
Rees-Mogg rounded off the rally by joking that the “Canada-style” free trade model backed by Brexiteers was even better than “Super-Canada”.
“It would be a SupercalifragilisticexpialidociousCanada,” he said, referring to the phrase in the movie ‘Mary Poppins’.
The Tories should “not fear” a Brexit on World Trade Organisation terms, Rees-Mogg added. It would be a “proper, red-blooded, Conservative approach to governing that frees the people from being tied down”.
“We have been Gulliver. Let us cut the ropes that the Lilliputians have tied onto us and show our giant form once again.”
Earlier, Grieve told the New Statesman that if May continued to rule out a fresh Brexit vote, she could be replaced by a new government drawing ministers from multiple parties.
The new national unity government would call a referendum but then disband itself after a few months.
“It would be fairly radical. Ultimately, any government is one which enjoys the majority of support of members of Parliament to carry out a policy. So, it would have to be on a cross-party basis.”