Theresa May has been plunged into a fresh Brexit crisis after anti-EU Tories rejected her ‘plan B’ attempt to rescue her deal and threatened to inflict another Commons defeat on Tuesday.

The prime minister took the extraordinary step of urging her MPs to back an amendment that “requires the Northern Ireland backstop to be replaced” – even though it effectively rips up her own agreement with the EU.

However, just 30 minutes earlier – in a dramatic underlining of her weakness – the hardline 60-strong European Research Group (ERG) rejected the wording as too vague.

Without ERG support, the amendment, tabled by Tory backbenchers’ leader Graham Brady, appeared doomed to fail – wrecking No 10 hopes that it would persuade the EU to give way.

Even before the setback, Brussels made clear it would, in any case, never accept a UK demand to replace the backstop, insisting the EU was “not going to reopen the agreement”.

Heidi Allen, a leading pro-EU Tory, said the prime minister was “dreaming” if she believed her strategy could succeed, telling The Independent: “She is doing nothing other than pandering to the ERG again.”

Despite the continuing stalemate, Ms May told the emergency meeting of Tory MPs that she wanted to stage a second “meaningful vote” on her deal by 13 February.

"Brexit betrayal" march in London Show all 43 1 /43 "Brexit betrayal" march in London "Brexit betrayal" march in London A protester holds an anti-BBC sign Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator holds a sign in the picket line Angela Christofilou/The Independent "Brexit betrayal" march in London A protester carrying a noose at the "Brexit betrayal" march. The man carrying it told a reporter: "That's what the traitor May deserves." AP "Brexit betrayal" march in London Pro-brexit supporters hold a sign opposed to Nigel Farage Angela Christofilou/The Independent "Brexit betrayal" march in London Protesters carry a defaced British flag on the march Angela Christofilou/The Independent "Brexit betrayal" march in London Tommy Robinson addresses a rally after taking part in a Brexit 'betrayal' march in central London PA "Brexit betrayal" march in London Police officers attempts to keep rival protesters from clashing at the Brexit 'betrayal' march in London Victoria Jones/PA "Brexit betrayal" march in London A protester holds an anti-Theresa May sign Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator and his dog Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator at the protest Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit sign at the rally Angela Christofilou/The Independent "Brexit betrayal" march in London Pro-brexit demonstrators endorse UKIP Angela Christofilou/The Independent "Brexit betrayal" march in London A Brexit 'betrayal' march protester wearing a Make Britain Great Again hat in London on 9 December 2018 Chris J Ratcliffe/Getty "Brexit betrayal" march in London Brexit 'betrayal' marchers gathering on Park Lane ahead of a protest Angela Christofilou/ The Independent "Brexit betrayal" march in London The "Brexit Betrayal" march passes through Central London Angela Christofilou/The Independent "Brexit betrayal" march in London Tommy Robinson tells protesters to join Ukip via their mobile phones on stage next to leader Gerard Batten (right) at the Brexit 'betrayal' march Gareth Fuller/PA "Brexit betrayal" march in London A protester speaks thorugh a megaphone on the march Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator walks in the picket line Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit anti-May sign at the rally Angela Christofilou/The Independent "Brexit betrayal" march in London A protester carries a Union Jack on the march Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator wrapped in the Union Jack Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit anti-May sign at the rally Angela Christofilou/The Independent "Brexit betrayal" march in London Pro brexit demonstrators move through Central London Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator marches with sign Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator holds a rude sign in the rally Angela Christofilou/The Independent "Brexit betrayal" march in London The march passes down Victoria Street near Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A festive protester marches near Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester holds a mock noose as the march passes down Victoria Street towards Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester wrapped in the Union Jack marches down Victoria Street towards Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester makes some noise on the march Angela Christofilou/The Independent "Brexit betrayal" march in London A protester dressed as a dinosaur holds a sign rallying against "Davocracy" - in reference to the annual World Economic Forum meeting in Davos Angela Christofilou/The Independent "Brexit betrayal" march in London A protester holds a pro-brexit sign on the march Angela Christofilou/The Independent "Brexit betrayal" march in London The march approaches parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester distributes pro-brexit lapel badges Angela Christofilou/The Independent "Brexit betrayal" march in London A demonstrator wears an anti-EU poster and holds an anti-BBC sign Angela Christofilou/The Independent "Brexit betrayal" march in London A smoke bomb is deployed in Parliament Square as the march comes across the counter-demonstration Angela Christofilou/The Independent "Brexit betrayal" march in London Angela Christofilou/The Independent "Brexit betrayal" march in London A flag bearing the Arms of Plantagenet flies in theprot Angela Christofilou/The Independent "Brexit betrayal" march in London Protesters on the Brexit 'betrayal' march in London on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Protesters on the Brexit 'betrayal' march in London on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Brexit 'betrayal' marchers gathering on Park Lane ahead of a protest on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Brexit 'betrayal' marchers gathering on Park Lane ahead of a protest on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Angela Christofilou/The Independent

Before that, the prime minister faces the embarrassment of another defeat on Tuesday, if the ERG stands by its threat to vote against Mr Brady’s amendment.

No 10 saw it as a mechanism of sending a clear message about the concessions the EU needed to make if the thumping 230-vote defeat on the divorce deal, a fortnight ago, is to be overturned.

But anti-EU Tories leapt on its vague suggestion for the backstop to be “replaced by alternative arrangements” – without setting out what they would be.

Jacob Rees-Mogg, the ERG chairman, said the group would stand firm, even if a whip is imposed, saying the amendment was “just an expression of opinion” without an alternative to the backstop.

Earlier, Sabine Weyand, the EU’s deputy chief Brexit negotiator, sought to kill any hopes of a rethink in Brussels, saying: “There’s no negotiation between the UK and EU – that’s finished.”

Ms Weyand ridiculed the Brady amendment for failing to “spell out what the alternative arrangements are”, saying: “We haven’t found them ... They don’t exist.”

She also warned the risks of a no-deal Brexit were rising, saying: “There’s a very high risk of a crash-out not by design, but by accident.”

Tuesday’s “next steps” debate will also see an attempt, led by Labour’s Yvette Cooper, to force the government to seek a nine-month Article 50 extension, if the Commons has not passed a deal by the end of February.

However, the radical attempt for parliament to “take control” – by passing its own legislation to delay Brexit – can only succeed if Jeremy Corbyn backs the amendment.

That support was cast into doubt when Jon Trickett, the shadow cabinet office minister and a key Corbyn ally, said it would be “ignoring the views of millions of ordinary folk”, by failing to respect the referendum result.

The warning raised the prospect of no amendments passing – leaving the UK still in dangerous limbo, with just 59 days until the 29 March deadline for withdrawal.

In the meeting of Tory MPs, Ms May also faced down Boris Johnson, after he challenged her on what difference the Brady amendment would make.

“We won’t know unless you support us Boris,” she told her former foreign secretary. “Get behind it and we will find out.”

One Tory MP described the exchange as the prime minister at her “spikiest”, adding: “It got one of the loudest cheers.”

Brandon Lewis, the Conservative party chairman, confirmed the Brady amendment would be whipped, saying: “It is about giving a message to Europe about what can go through parliament in terms of dealing with the backstop issue.”

Ms May had insisted the backstop is unavoidable, telling MPs in November: “There is no alternative deal that honours our commitments to Northern Ireland which does not involve this insurance policy.”

The latest Westminster drama came as supermarkets issued a stark warning they could run out of food and be forced to hike prices if the UK crashes out of the EU with no deal.

Nine senior executives signed an open letter to MPs, organised by the British Retail Consortium (BRC), arguing items with disappear from supermarket shelves.

Meanwhile, Matt Hancock, the health secretary, told MPs that medicines “will be prioritised” over food if a no-deal Brexit disrupts supply chains.