Pro- and anti-EU Tories are putting pressure on Theresa May to accept a Brexit ‘plan C’, after joining forces in a remarkable secret compromise.

Remainers including current ministers have struck a deal with hardliners Jacob Rees-Mogg and Steve Baker to deliver EU withdrawal on 29 March, while preventing an implosion of the warring Conservative party.

It is unclear whether the prime minister endorsed the talks – although Nicky Morgan, the pro-EU former education secretary who played a key role, insisted she did know about them.

Furthermore, the plan – which involves replacing the current Irish backstop and a longer transition period even if the EU refuses – seems certain to be rejected in Brussels, even if adopted by the government.

Nevertheless, Ms Morgan argued it could succeed, saying: “People like me want to avoid a no-deal outcome, a crashing out on 29 March. We have to look for ways to do that. We are all prepared to compromise on that.”

Mr Baker, the deputy chairman of the anti-EU European Research Group, said: “We need to get out of the EU on time and with a functioning government. This is how.”

Liam Fox, the international trade secretary, declined to set out the government’s view, but said ministers were “open to listening to all ideas”.

But Ben Bradshaw, a Labour MP campaigning for a Final Say referendum, condemned it as unrealistic, tweeting: “More time-wasting, chasing more unicorns, which makes a crash-out no-deal Brexit more likely.”

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Under the proposals, the prime minister would seek to renegotiate the backstop – designed to prevent the return of Irish border checks – based on a reliance on unproven technology.

If that failed, the EU would be asked to still grant the cushion of a transition period, extended to December 2021, in return for the UK paying the full £39bn divorce bill and protecting EU citizens’ rights.

This would give both sides time to prepare for a hard Brexit departure on World Trade Organisation (WTO) terms at the end of 2021 – or to strike a trade deal to kick in at that time.

However, as recently as November, Michel Barnier, the EU’s Brexit negotiator, told the UK: “Without an operational backstop, there will not be an accord and there will not be a transition period. That is certain.”

The Democratic Unionist Party then announced it backed what has been dubbed the “Malthouse Compromise” - after the minister, Kit Malthouse, who brokered it - piling further pressure on Ms May to do the same

“We believe it can unify a number of strands in the Brexit debate including the views of Remainers and Leavers. It also gives a feasible alternative to the backstop proposed by the European Union,” said Arlene Foster, the DUP’s leader.

The new Brexit twist came ahead of a crucial Commons debate, which could see MPs vote to force the government to seek a nine-month Article 50 extension, if no deal has been passed 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.

Late on Monday, Ms May threw her weight behind an amendment that “requires the Northern Ireland backstop to be replaced” – even though it effectively rips up her own agreement with the EU.

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

Dr Fox urged Tory MPs to step into line, confirming the prime minister would then seek to reopen the withdrawal agreement to give any change legal force.