THERESA May was last night battling to hold together a “catastrophic split” within her party as she appealed to warring members to back her controversial Brexit blueprint and avoid a disorderly withdrawal from the EU which would damage Britain's interests.

It comes as it emerged former foreign secretary Boris Johnson – who dramatically quit last week – is being urged to attack the Prime Minister in an explosive resignation speech aimed at booting hard-line Brexiters.

The influential 1922 Committee of backbench MPs has reportedly amassed 40 letters demanding a vote of no confidence in Mrs May – eight shy of the threshold needed to trigger a ballot.

But despite an excruciating week that saw US President Donald Trump humiliate the Prime Minister by criticising her Brexit approach, while seven senior Tories stood down over her Chequers plan for a softer Brexit, even ardent Eurosceptics are calling for a “change of policy, not a change of leader”.

Last night Mrs May suffered her eighth resignation over Brexit, as Tory MP Robert Courts – who sits in former prime minister David Cameron’s old seat – stepped down as a ministerial aide. He insisted: “I had to think who I wanted to see in the mirror for the rest of my life.”

Meanwhile, it emerged Eurosceptics have set up a “party within a party” in a bid to circumvent Tory whips and further frustrate Mrs May’s plans.

Ahead of a crucial week in Parliament, the Prime Minister acknowledged feelings in the party were running high, but said her blueprint offered a practical way forward.

She said: "Many people voted from the heart to leave the European Union. My job as Prime Minister is to deliver for them, but also I've got to be hard-headed and practical about this and do it in a way that ensures we get the best interests for the UK."

Speaking to the BBC, she also revealed the “brutal” advice given to her by Mr Trump following the Brexit vote, which the president alluded to in an extraordinary joint press conference on Friday.

She said: "He told me I should sue the EU – not go into negotiations, sue them."

SNP MEP Alyn Smith branded the suggestion “demonstrable rubbish”, and accused Mr Trump of being “the worst sort of pub bore sounding off about something he does not understand”.

Leading Brexiter Jacob Rees-Mogg warned trust in Mrs May was waning amid acrimonious claims key ministers, including former Brexit Secretary David Davis, were kept in the dark about her proposals.

In a scathing aside, he accused her of failing to embrace the opportunities of Brexit, saying she was "a Remainer who remained a Remainer".

Meanwhile, Mr Davis, who resigned just days after signing up to the Chequers plan last weekend, accused Mrs May of being "astonishingly dishonest" for claiming there is no alternative to her proposals.

His former Brexit minister Steve Baker said she had presided over a "cloak and dagger" plot to pursue a much softer exit from the EU than he and Mr Davis thought they were working towards.

He said the Tory party faces a "catastrophic split” that “cannot be reconciled".

Tory MPs from northern English constituencies have also warned the Chequers plan has "gone down like a lead balloon" with voters.

Over the weekend, one poll put Labour four points ahead of the Tories, while support for Ukip rose by five points.

MPs are today due to vote on a series of amendments to the Customs Bill tabled by members of the European Research Group (ERG), which Mr Rees-Mogg leads, intended to scupper Mrs May’s plans for a "UK-EU free trade area" based on a "common rule book".

With no Labour backing, the changes stand little chance of getting through, although the votes could provide Tory Brexiters with the opportunity to stage a show of strength in Parliament.

Another potential flashpoint comes with speculation Mr Johnson, who quit as foreign secretary in protest over the Brexit plans last Monday, is preparing to make a resignation statement in the Commons. Some are urging him to use it to attack Mrs May and help trigger a no confidence vote.

The Prime Minister could face a further challenge on Tuesday, this time from pro-EU Tories seeking to amend the Trade Bill to keep the UK in a customs union with the EU.

She said she had been forced to come forward with her revised proposals after the EU had offered two options: either the UK remain in the customs union and accept continued freedom of movement, or Northern Ireland would effectively be "carved out" from the UK. Neither of these was acceptable.

Mrs May said: "Faced with that we had an option. We could go for no deal, no deal is still there, it is still possible, but I think the best thing for the UK is to have deal that sets a good relationship with our trading partners in the future.

"So if we were going to find something that was in Britain's interest, that delivered on the referendum and that was negotiable, we had to make what is a compromise but is a positive in terms of the benefits it gives us."

She said the plan would avoid the need for a hard border between Northern Ireland and the Republic, maintain "frictionless" trade with the EU, and still allow the UK to negotiate free trade deals with other countries.

But despite playing down the prospect of an imminent leadership challenge, Mr Rees-Mogg insisted the Prime Minister's approach to the Brexit negotiations had been “hopeless”.

He warned Mrs May risked splitting the party unless she changed course, adding: "Brexit is enormously positive, a huge opportunity for the country. I'm afraid the Prime Minister doesn't see that.

"It is a worry that the Prime Minister was so clear that Brexit meant Brexit and that she had her red lines and these have now gone.

"Trust is to some extent at the heart of policy making so that does concern me."