The EU's chief Brexit negotiator Michel Barnier has insisted he will not scrap the Irish backstop.
Mr Barnier, writing in the Sunday Telegraph, insisted the measures, aimed at preventing a hard border across Ireland, represented the "maximum flexibility" that Brussels can offer.
However Prime Minister Boris Johnson has branded the current Withdrawal Agreement, with the Irish backstop, unacceptable.
Mr Johnson has launched a war of words against would-be Tory Brexit rebels ahead of a showdown Commons clash.
As Downing Street ratcheted-up the rhetoric, ministers branded a cross-party alliance of MPs seeking to prevent a no-deal Brexit as “deceitful and underhand”.
Tory heavyweights like ex-chancellor Philip Hammond reacted angrily to claims Conservative MPs voting against a no-deal option when parliament returns this week could be barred from standing in a snap general election.
In his first newspaper interview since becoming Prime Minister in July, Mr Johnson told the Sunday Times: “I just say to everybody in the country, including everyone in parliament, the fundamental choice is this: are you going to side with Jeremy Corbyn and those who want to cancel the referendum?
“Are you going to side with those who want to scrub the democratic verdict of the people – and plunge this country into chaos.”
The comments came ahead of an expected Commons clash on Tuesday when opponents of no- deal look set to try and seize control of the parliamentary agenda to push through legislation that would force the PM to seek a Brexit extension from Brussels beyond October 31.
A staunch ally of the prime minister and Leader of the Commons Jacob Rees-Mogg strongly attacked such an action.
Writing in the Mail on Sunday, Mr Rees-Mogg said: “They dare not use the confidence procedures because they know that Jeremy Corbyn is too unpopular, and therefore they seek deceitful ends by underhand means.”
Reports that any bid to extend Brexit to stop a no-deal exit would be treated as a no confidence issue, with supporting Tory MPs stopped from standing for the party, drew a harsh response from Mr Hammond.
The ex-chancellor tweeted: “If true, this would be staggeringly hypocritical: 8 members of the current cabinet have defied the party whip this year.
“I want to honour our 2017 manifesto which promised a “smooth and orderly” exit and a “deep and special partnership” with the EU.
“Not an undemocratic No Deal.”
A Government spokesperson said: “All options for party management are under consideration, but first and foremost the PM hopes MPs will deliver on the referendum result and back him on Parliament.”
Some 20 Tory former ministers are considering standing at the next election as independent Conservatives rather than back a no-deal option, the Sunday Times said.
Tens of thousands of protesters demonstrated against Mr Johnson’s plans to suspend Parliament for up to five weeks ahead of the return of MPs from their summer recess on Saturday.
Meanwhile, controversy is brewing over the abrupt sacking of Chancellor Sajid Javid’s special adviser Sonia Khan by the PM’s key aide Dominic Cummings continued.
It is understood that the Chancellor was not informed of the dismissal beforehand and Ms Khan was escorted out of Downing Street by a police officer after being fired.
Yvette Cooper, the Labour chair of the House of Commons home affairs select committee, told The Observer: “Government advisers must not abuse their power by drawing the police into heavy- handed political stunts. This needs to be reviewed by the cabinet secretary and the Metropolitan police straight away.”
Mr Johnson said that Wednesday’s planned departmental funding announcement for 2020/2021 would see the “biggest, most generous spending review since the height of Tony Blair’s New Labour”.
Local authorities will get a £3.5 billion boost, including £1 billion for social care, in the spending round, according to the Sunday Times.