International Trade Secretary Liam Fox has urged Tory MPs to give Theresa May a “strong mandate” to return to Brussels to negotiate changes to the controversial Northern Ireland backstop.

Ahead of a series of Commons votes which could help shape the next phase of talks with the EU, Mr Fox said the Prime Minister was ready to reopen the Brexit Withdrawal Agreement in order to secure a legally-binding text.

At a meeting of Tory MPs in Westminster on Monday, Mrs May called on them to get behind an amendment tabled by influential chairman of the backbench 1922 Committee Sir Graham Brady calling for “alternative arrangements” to the backstop.

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Theresa May is urging MPs to back changes to the Irish backstop (House of Commons/PA)

Conservative MPs were informed that they would be whipped to vote for the amendment – assuming it is selected by Commons Speaker John Bercow.

Her hopes of gaining a Commons majority for the plan received an initial setback after Jacob-Rees-Mogg, the leader of the pro-Brexit European Research Group (ERG), said they were not prepared to support it and it did not change anything.

However, he suggested that he could be prepared to support it if the amendment had official Government backing.

“Let’s see what the Prime Minister says at the despatch box today and what the Brady amendment really means,” he told the BBC.

“If the Brady amendment is a Government amendment, effectively, that means the Withdrawal Agreement will be reopened; that’s very different from a worthy backbench motion that doesn’t do anything.

“So let’s just wait and see on that.”

The ERG’s rejection had come after former foreign secretary Boris Johnson appeared to suggest he could back Sir Graham’s amendment – although he was later reported to have been involved in a series of sharp exchanges with Mrs May on the issue at Monday’s meeting.

Mr Fox, however, insisted that backing the amendment would strengthen the Prime Minister’s hand when it came to reopening negotiations on the backstop – intended to ensure there is no return of a hard border on the island of Ireland.

“I think we should send the Prime Minister back to Brussels with a strong mandate to be able to say if you compromise with us on this one issue, on the backstop, we would be able to a get an agreement – an agreement that is almost there,” he told BBC Radio 4’s Today programme.

Both the EU and the Irish government have been adamant that there can be no question of reopening the Withdrawal Agreement.

Ireland’s European Affairs Minister, Helen McEntee, said: “There can be no change to the backstop. It was negotiated over 18 months with the UK and by the UK. A bit of realism is needed at this stage.”

However, Mr Fox said he believed attitudes on the EU side on the need to find a compromise were changing in the light of the growing economic uncertainty.

“We have seen the German economy weakening, we have seen the French economy weakening,” he said.

“I think this view – ‘We can simply weather out any disturbance that would occur from a no-deal’ – I think there is much less appetite for that. I think we still have time to reach a compromise on that.”

Mr Fox reacted coolly to a compromise plan drawn up by MPs from the Leave and Remain wings of the Conservative Party, in talks co-ordinated by MP Kit Malthouse.

Former Cabinet minister Nicky Morgan said discussions had been taking place for “some days” between herself, health minister Stephen Hammond, and Solicitor General Robert Buckland on one side and Mr Rees-Mogg and Steve Baker from the ERG on the other.

Their plan involved a “recasting” of the Northern Ireland backstop as “free trade agreement-lite” with a commitment on all sides there should be no hard border on the island of Ireland and an extended transition period to December 2021.

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Nicky Morgan is working on a compromise plan by Leave and Remain Tories (Lauren Hurley/PA)

“The Prime Minister has been aware of the discussions. At some point there has to be compromise on all sides in order to get a deal over the line. That is what most of us want to see – a negotiated settlement with the EU,” Ms Morgan told the BBC Radio 4 Today programme.

“People like me want to avoid a no-deal outcome, a crashing out on March 29. We have to look for ways to do that. We are all prepared to compromise on that.”

Former party leader Iain Duncan Smith, from the Brexiteer side, said the plan represented the “best hope” for the Conservatives.

“I really urge the Government to embrace this because what this will tell the European Union is that now, I believe, a majority of Parliament, particularly in the governing party, have agreed there are compromises to be made,” he said.

However, Mr Fox said: “There are all sorts of ideas being put out, but Parliament cannot take a decision unless it is on the order paper and it is not on the order paper.”