Boris Johnson backs Jacob Rees-Mogg in Brexit split with Theresa May

The Foreign Secretary tweeted his support of Jacob Rees-Mogg after the arch-Brexiteer had issued a warning to Theresa May Credit: PA

Boris Johnson has leapt to the defence of a prominent critic of Theresa May as Tory infighting over Brexit intensified ahead of crunch Cabinet talks on the UK’s exit strategy.

The Foreign Secretary said MPs should be "able to air their views" after Jacob Rees-Mogg was criticised for saying the Prime Minister must deliver the Brexit she promised or risk collapsing her Government.

Mr Johnson’s intervention on Twitter on Monday also appears to put him at odds with a minister in his own department - Sir Alan Duncan earlier accused Mr Rees-Mogg of "insolence".

Mr Johnson said: “It’s vital that all MPs are able to air their views on Brexit.

“Whatever your position, I hope we can all agree that Jacob Rees Mogg is a principled and dedicated MP who wants the best for our country.”

Mrs May has faced repeated warnings that senior figures in her government are on manoeuvres in preparation for a leadership battle.

Brexiteer Mr Rees-Mogg, tipped as a potential Tory leader, had used an opinion piece in Monday’s Daily Telegraph to warn the Prime Minister she must deliver what she promised – the UK leaving the single market and customs union and outside the jurisdiction of the European Court of Justice – or risk her administration.

He insisted he was “confident” Mrs May would deliver the Brexit she had promised, but warned the PM that backsliding could result in splitting the party like Sir Robert Peel, who plunged it into the political wilderness for nearly three decades following bitter divisions over trade reforms.

The chairman of the European Research Group of Brexit-backing Tories said: “Theresa May must stand firm for what she herself has promised.

“One former Tory leader, Sir Robert Peel, decided to break his manifesto pledge and passed legislation with the majority of his party voting the other way.

“This left the Conservatives out of office for 28 years.

“At least he did so for a policy that works. At Chequers (Mrs May) must stick to her righteous cause and deliver what she has said she would, she must use her undoubted grace to persevere.”

Mr Rees-Mogg’s intervention prompted a furious backlash from Remain-voting Tories.

Foreign Office minister Sir Alan said his comments risked “debasing” the Government, Tory Party and the country as a whole, saying: “The ideological right are a minority despite their noise and should pipe down.”

North Dorset MP Simon Hoare said “the hectoring nonsense” and “blackmail” had to stop and urged his party to wake up to the potential “calamity” of a Jeremy Corbyn-led government.

Tory MP Vicky Ford – a former MEP and supporter of close ties to Europe – told BBC Radio 4’s Today programme: “What I would say to Jacob… is if this becomes a binary choice between staying in the single market and customs union or no deal, then I do not believe there is a majority for no deal.”

But former Conservative leader and Brexiteer Lord Howard told Today: “The Prime Minister has made a series of promises, the Prime Minister has repeatedly said that we must regain control of our laws, our money and our borders.

“I have great confidence in the Prime Minister. I am sure that she will deliver a Brexit that is entirely consistent with the promises she has made.”

The row comes after the PM’s chief Brexit official reportedly told ministers they have no chance of striking a bespoke trade deal with Brussels.

Briefing Cabinet ministers ahead of the Chequers talks, Oliver Robbins is said to have painted a bleak picture of the situation, with a source telling The Times they came out of the meeting thinking “we were even more screwed than we were before”.

Mrs May will bring together her Cabinet at her country residence to thrash out details of a white paper setting out the UK’s plans for areas such as trade.

Brexiteers oppose the PM’s favoured option of a customs partnership with the EU, which would see the UK collect tariffs set by the EU customs union on goods entering the country on behalf of the bloc.

Their “max fac” alternative would, rather than scrapping customs checks, use technology to minimise the need for them.

Both options have been dismissed by the EU.

The Prime Minister will assemble her Cabinet at her Chequers country retreat for talks on Brexit Credit: Suzanne Plunkett/PA

According to the BBC, No 10 has produced a third model for handling customs after Brexit which will be discussed by senior ministers at the gathering on Friday.

Theresa May called on EU leaders to show flexibility and look “seriously” at the UK’s Brexit plans as Tory infighting over Europe intensified ahead of crunch talks at Chequers.

Mrs May said next week’s Government’s white paper would set out “detailed proposals for a sustainable and close future relationship” between the UK and EU and mark “an important step in delivering the decision of the British people”.

Addressing MPs in the Commons on Monday afternoon, after a meeting with DUP leader Arlene Foster, Mrs May again stressed the UK would leave the single market and customs union.

She said: “The EU and its member states will want to consider our proposals seriously.

“We both need to show flexibility to build the deep relationship after we have left that is in the interests of both our peoples.”