THERESA May faces a crucial day in the Commons that could carve the shape of Brexit, with fewer than 60 days remaining until the UK is due to leave the EU.

Amid an ongoing revolt among backbenchers and her DUP allies, the Prime Minister has swung behind a motion amendment that would allow her to go back to Brussels and seek changes to the Irish border backstop.

She will whip MPs to support the amendment tabled by 1922 Committee chairman Sir Graham Brady, which states that Parliament would be willing to support the Withdrawal Agreement reached with the EU if "alternative arrangements" were found to avoid a hard border.

The dramatic move is far from guaranteed to deliver a majority for the plan after it failed to win the support of the influential European Research Group (ERG) of Conservative Eurosceptics, who have not ruled out voting against it.

There is also the small matter of the amendment being called by Commons Speaker John Bercow on Tuesday morning, although his hand may be swayed by the number of MPs backing it already.

Tory grandee Sir Graham said he hoped House of Commons backing would give Mrs May "enormous firepower" when she returns to Brussels to seek concessions on her Brexit deal.

But the chairman of the ERG, Jacob Rees-Mogg, said its members, thought to number at least 60, will not support the scheme.

Meanwhile, late on Monday evening it emerged a new Brexit plan had been put forward which is reportedly backed by members of both the Remain and Leave camps of the Conservative party.

The plan - called the The Malthouse Compromise after Kit Malthouse, the MP who brought the parties together - would lead to Britain leaving the EU "on time and with a functioning government", former Brexit minster Steve Baker said.

Said to be drawn up by Nicky Morgan and supported by others, the plan reportedly "provides for exit from the EU on time with a new backstop, which would be acceptable indefinitely, but which incentivises us all to reach a new future relationship".

It would extend the transition period - the period where the UK would continue to follow EU rules and pay into its budget - from the end of 2020 and into December 2021 which would "allow both parties to prepare properly for WTO terms, but also provide a period in which the parties could obviate this outcome by negotiating a mutually beneficial future relationship".

Mrs May addressed MPs in Westminster on the eve of a day of high drama, when MPs will debate a range of rival amendments, including calls to block a no-deal departure or delay Brexit from its scheduled date of March 29.

Conservative chairman Brandon Lewis, who confirmed the whipping after the meeting, said the Brady amendment would "allow the Prime Minister to give a very clear message around what Parliament wants, where the party is".

He said: "I would hope the ERG, when they look at this and actually look through the detail of what this gives the PM tomorrow, (see) it is about giving a message to Europe about what can go through Parliament in terms of dealing with the backstop issue and why that matters."

Mr Lewis confirmed that the Government would whip against an amendment co-sponsored by one of its own MPs, Nick Boles, which seeks to extend the Article 50 period to avoid a no-deal Brexit.

Despite the manoeuvring in Westminster, in Brussels the EU, officially at least, remained resolute that the Withdrawal Agreement would not be reopened.

Chief EU negotiator Michel Barnier's deputy Sabine Weyand warned there was a "high risk" of the UK crashing out by accident, as it was "quite a challenge" to see how a majority could be constructed at Westminster.

European Commission vice-president Jyrki Kateinen said there was "no reason to give any concessions" to the UK and there was "not much room for manoeuvre" on the backstop.

It would be "stupid" for the EU to make concessions putting the remaining 27 members at a disadvantage simply to secure a deal, he said.

What happens and when?

  • The debate in Parliament gets underway at 12.30pm
  • Voting on the plan will start at 7pm

Downing Street said the PM remains committed to quitting the EU on March 29 and will take her plan back to the Commons for a second "meaningful vote" as soon as possible after Tuesday's debate.

The developments came as major supermarkets and fast-food chains warned that a no-deal Brexit would force up prices and reduce the choice and quality of produce for shoppers.

In a joint letter, bosses of firms including Sainsbury, Asda, KFC and McDonald's said: "We anticipate significant risks to maintaining the choice, quality and durability of food that our customers have come to expect in our stores, and there will be inevitable pressure on food prices from higher transport costs, currency devaluation and tariffs."