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Boris Johnson was today scrambling to win over a handful of MPs whose votes could save his Brexit deal from being defeated in the Commons tomorrow.

The Prime Minister returned to 10 Downing Street at 3am from the Brussels summit after being warned by Tory whips that the vote during the first Saturday sitting in four decades will be “desperately close”.

But his charm offensive met two setbacks. In the first, Labour MPs were explicitly threatened with losing their jobs if they back Mr Johnson tomorrow.

Secondly, Tory Right-wingers dropped a bombshell by saying that the PM’s deal would allow them to cause Britain to crash out on “no deal” terms in a year’s time even if it is passed.

The Evening Standard can reveal that members of the European Research Group of hardline Eurosceptics are seeking advice from the Attorney General to support their view that if no trade deal is agreed with the EU by the end of 2020, Britain could switch by default from full EU rules to World Trade Organisation terms.

Their demands were revealed by Right-winger John Baron, who said that Mr Johnson’s deal was “a fundamental improvement” on Theresa May’s rejected agreement precisely because “what it means is ... if there’s no deal struck in the transition period up to December 2020, the UK has the right, with the Northern Ireland provisions in place, to leave on no deal terms”.

He told the BBC: “Most colleagues in the House prefer a good deal to no deal. But the best way of getting a good deal is by keeping no deal on the table. And that is the fundamental difference between Theresa May’s backstop and Boris Johnson’s backstop.”

Responding to Mr Baron’s claim, a source close to Mr Raab said: “I don’t recognise that.”

His claim caused alarm among Opposition MPs being wooed by the Prime Minister, who was thought to need at least a dozen Labour rebels to come behind him to get the deal through.

Former Tory defence minister Guto Bebb said: “John Baron has let the cat out of the bag. He admits that he and many of his fellow ideologues in the extremist Conservative faction of the ERG are supporting Boris Johnson’s Brexit proposals only because they see it as the fastest way to fulfil their no-deal fantasies.”

Liberal Democrat Tom Brake said: “The cut and paste job done to the withdrawal agreement shows Boris Johnson’s intent — his deal seriously undermines the UK.”

Mr Johnson flew back early from the EU summit to take personal charge of the battle to secure votes. The Prime Minister rose after five hours sleep to meet aides at 9am and plan a series of phone calls and meetings with MPs.

The PM’s battle plan was described as targeting Tory MPs from the ERG, potential Labour rebels and also offering a potential return of the Tory whip for the 21 Conservatives who rebelled in September to stop no-deal.

No 10 sources said Mr Johnson was also reaching out to the DUP despite a furious denunciation of his deal by the Northern Irish party’s Brexit spokesman Sammy Wilson, who said it was “siphoning off” Northern Ireland from the UK.

Some of the ERG “Spartans”, including former Northern Ireland secretary Owen Paterson and backbencher Julian Lewis, were today undecided about whether to back the deal or not.

Mr Johnson is targeting 28 ERG members who refused to back Mrs May’s thrice-rejected deal. Tory MPs said he needed the vast majority to swing behind him to stand any chance of winning the vote.

Shadow chancellor John McDonnell warned there could be “consequences” for any Labour MPs who break ranks. However, veteran Graham Stringer, who voted three times against Mrs May’s deal, said: “It’s a bad deal but if I thought that we would not get Brexit at all then I would consider voting for it.”

Labour MPs Ronnie Campbell, John Mann, Ruth Smeeth and Caroline Flint have indicated they could be persuaded.

But in a hostile intervention, Labour grandee Jon Lansman, the Momentum founder, said they would be sacked if they did. He said: “Johnson’s deal will be a wrecking ball through the lives & well-being of ordinary people across Britain. Labour MPs cannot and must not vote for it. If they do, the NEC will have no choice but to replace them with a new, socialist Labour candidate at the next election.” Fellow NEC member Huda Elmi backed him, saying: “Any Labour MP that sides with Johnson has no right to stand at the next election.”

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