The Prime Minister will chair a meeting of the Cabinet in Downing Street today (Sept 24) amid intense pressure to change course and seek a simpler, less ambitious deal.
The meeting will take place just hours after the high-profile launch of an alternative plan for leaving the EU by the free market Institute of Economic Affairs think tank with the backing of former foreign secretary Boris Johnson and former Brexit secretary David Davis.
In his weekly column for The Daily Telegraph, Mr Johnson warned it would play into the hands of Jeremy Corbyn and the Labour Party if the Government continued to pursue the same course in the facing of rising public hostility.
“If we go with the Chequers approach, the public will spot it.
“They will see that the UK has become a vassal state, that we have not taken back control, but lost control.
“They will take their revenge at the polls,” he wrote.
“I am afraid that Chequers = surrender; Chequers = a sense of betrayal; Chequers = the return of Ukip; Chequers = Corbyn.”
The meeting was called in part to discuss post-Brexit immigration policy after an expert report recommended EU nationals should be subject to the same rules as migrants from the rest of the world once Britain has left the bloc.
However there is likely to be a lengthy inquest into what went wrong at last week’s informal EU summit in Salzburg where Mrs May was bluntly told key elements of the Chequers plan would not work.
The Prime Minister insists her proposal, which would see Britain maintain a “common rulebook” with the EU for trade in goods and agriculture, is the only credible option on the table which would avoid the return of a “hard border” between Northern Ireland and the Republic.
But she is facing increasingly vociferous calls from Tory Brexiteers to abandon Chequers in favour of a more basic free trade agreement in goods along the lines agreed between the EU and Canada.
Over the weekend Foreign Secretary Jeremy Hunt, seen as a May loyalist, pointedly refused to rule out the prospect that the Government could switch its negotiating position in favour of a Canada-style deal.
Home Secretary Sajid Javid, International Trade Secretary Liam Fox, International Development Secretary Penny Mordaunt, the Leader of the Commons Andrea Leadsom and Work and Pensions Secretary Esther McVey are all reported to have concerns about Chequers.
Brexit Secretary Dominic Raab, however, warned that Brussels’ offer of a Canada-style deal would mean agreeing to customs controls between Northern Ireland and the rest of the UK, something Mrs May has flatly rejected.
Meawhile The Times reported Mr Javid was set to further anger Brexiteers that new controls should not be imposed on EU migrants for more than two years in the event of a no-deal break in order to protect the economy.
The pressure on the Prime Minister intensified with the confirmation over the weekend by Mr Corbyn that Labour will vote against any deal based on Chequers in the Commons.
With a bloc of Tory Brexiteers also committed to opposing the plan, and a number of pro-EU MPs also highly critical, it is increasingly difficult to see how she can muster the numbers to get it through Parliament, even it she can get an agreement with the EU.
With the Conservative Party conference next week in Birmingham looming, Downing Street was forced to deny she was planning a snap general election in an attempt to save her beleaguered premiership.
It followed weekend reports that two senior aides had responded to her Salzburg rebuff by “wargaming” an autumn vote to win public backing for a new plan.
Mr Raab said the idea of a snap election was “for the birds” and that the Government would continue negotiating with the EU.
At the same time he said they were continue to prepare for a no-deal break with the publication on Monday of a third tranche of “technical” papers on the preparations taking place across various sectors.