Boris Johnson had secret talks with Cabinet rebel Michael Gove last week on whether to defy David Cameron over the EU referendum, The Mail on Sunday can reveal.

The two dined at the London Mayor’s home on Tuesday, where they agreed the Prime Minister’s new EU deal was ‘thin’.

Shortly afterwards, Justice Secretary Mr Gove shocked No 10 by joining the ‘Out’ campaign to cut Britain’s ties with Brussels.

The disclosure of the secret dinner – and the pair’s sharp criticism of the outcome of Mr Cameron’s negotiations – will fuel speculation about which side Mr Johnson will back in the forthcoming EU referendum.

He is said to have told a Westminster contact: 'I'm veering all over the place like a shopping trolley.'

Left, Boris Johnson's wife, lawyer Marina Wheeler - an outspoken critic of the PM's deal - leaves the family home before Michael Gove arrives. Right, a smiling Justice Secretary emerges from Boris's front door

Left, perhaps the pair were expecting a long, sweaty discussion to rival the EU negotiations, as a courier arrives to deliver new shirts. Right, the meeting was also attended by Mr Gove's wife, Sarah Vine

According to Tim Shipman at The Sunday Times, one source close to Mr Johnson said: 'It’s a very difficult call for him. He is really conflicted. I think his heart is for out, but there is an enormous amount of pressure.'

Another Tory source said: 'Cameron is absolutely furious with Boris. He has had all the perks, visits to Downing Street and he still won't commit.'

Yesterday, Mr Gove and five fellow Ministers staged a dramatic revolt at a crisis Cabinet meeting on the referendum – the first time the Cabinet has assembled on a Saturday for more than half a century.

Friends of the Mayor said last night he was still ‘agonising’ over his stance on the issue.

He is said to be concerned that if he fails to back Mr Cameron it could hurt his chances of securing a big cabinet job, potentially as foreign secretary, after the EU referendum.

Today, Mr Johnson's sister said he was not 'milking' his decision over Britain's membership of the European Union for 'maximum publicity'.

Writer and broadcaster Rachel Johnson said her brother had to make a 'very, very hard' choice as there are good and bad arguments on both sides.

She added that Mr Johnson's presence in either the Remain or Leave campaign will be 'very significant' - which is why he is taking so long to decide.

IS HE TRYING TO TELL THE FUTURE? Mr Gove could hardly have been reading a more fitting manual as he wrestled with his decision to join the Leave campaign. Spotted in his bag was Superforecasting: The Art And Science Of Prediction. The book, by Canadian psychology professor Philip Tetlock and journalist Dan Gardner, explores how talented amateurs are able to predict the outcome of events that leave experts stumped. Difficult questions in the book that people were asked to predict include: ‘In the next year will any country withdraw from the eurozone?’ Advertisement

The London mayor is expected to reveal his intentions at 10pm on Sunday.

Ms Johnson also dismissed suggestions from presenter June Sarpong, of Britain Stronger in Europe, that it would be the 'ultimate betrayal' to London if the city's mayor decides to support Britain's exit from the EU.

Ms Johnson told Murnaghan on Sky News: 'I think that June's absolutely wrong to talk about this being an ultimate betrayal, and this is not in any sense Boris milking his decision for maximum publicity.

'This is an enormously complicated decision for everybody, not just Boris... and his participation in either camp is going to be very significant, and this is why he's taking so long to decide.

'The deal came through on Friday and perhaps you can imagine it's a very, very hard choice that he has to make, and in fact it's a hard choice for everybody to make because there are good and bad arguments on both sides.'

When it was suggested Mr Johnson is 'on the horns of a dilemma', Ms Johnson replied: 'Of course he is, and it is agonising.'

No 10 aides fear that if Mr Johnson follows Mr Gove’s surprise ‘defection’ to the ‘Out’ camp, the two formidable politicians could inflict a humiliating defeat on Mr Cameron.

However, there is better news for the Prime Minister today as a new poll shows the ‘In’ campaign has surged into a 15-point lead.

According to the Survation poll for The Mail on Sunday, 48 per cent of voters want to stay in the EU, with 33 in favour of leaving, and 19 per cent undecided. The first survey conducted since Mr Cameron’s marathon talks in Brussels on Thursday and Friday also found that 35 per cent believe he did well in the negotiations, against 30 per cent who say he did badly.

Mr Gove’s meeting with Mr Johnson started after the Justice Secretary arrived at the Mayor’s home in Islington, North London, at 8pm on Tuesday. He did not leave until 11.30pm. A well-placed source said the two men agreed that they were both ‘disappointed’ by the outcome of Mr Cameron’s attempts to win back powers from Brussels.

In particular, they felt let down by the way that Mr Johnson’s call for the Prime Minister to find a way to enshrine the supremacy of the British Parliament over the EU had only achieved limited success.

Mr Cameron’s inclusion of the topic in the talks was seen by many as a ploy that could pave the way for Eurosceptic Mr Johnson to endorse the Prime Minister for having heeded his suggestion. But Mr Gove, the Minister tasked with making such moves legally watertight, privately admitted the plans were impractical: it was one of the main reasons he decided to back the ‘Out’ campaign.

Boris Johnson leaving his home later in the week, with his bicycle, and right, his plush home

Mr Gove was accompanied by his journalist wife Sarah Vine, while Mr Johnson’s wife – human rights lawyer Marina Wheeler – had been at the house earlier that evening.

In a scathing magazine article two weeks ago, Ms Wheeler said the Prime Minister had done precious little to limit the ‘untenable’ power of the European Court of Justice. The supposed reassurances the PM secured with Brussels ‘raise more questions than they answer,’ she said. Mr Johnson’s aides stressed his wife was speaking in a personal capacity, but her outspoken view was said by some to reflect her husband’s opinion.

Mr Johnson is expected to announce in the next 24 hours if he will stand with Mr Gove in the ‘Out’ campaign, or with Mr Cameron in the ‘In’ campaign.

The Mail on Sunday revealed earlier this month that when a fellow Eurosceptic Conservative MP accused Mr Johnson of ‘wimping out’ of backing the ‘Out’ camp, the Mayor protested: ‘I’ve never been an Outer.’

Other MPs say Mr Johnson is ‘genuinely torn’ over the issue. One senior Tory said last night: ‘The danger for Boris in backing Gove is that it will be seen as an attempt to depose Cameron as PM. The danger for him in backing the PM is that no one will take him seriously as a Eurosceptic ever again.’ And a former Tory Minister cast doubt on whether Mr Johnson would back the ‘Out’ campaign. ‘It may all have been choreographed by No 10 as a dramatic way to show Boris is backing Dave after all,’ said the MP.

WHO SAID WHAT ON THAT DEAL ‘Britain banged the table and aggressively demanded the status quo. The EU, after some mandatory faux-agonising, agreed.’ Tory MEP Dan Hannan ‘Is this delay in Brussels just so that Cameron can serve up Eton Mess for pudding?’ Labour MP Chris Bryant ‘Oh, let’s give them a few little morsels so they’ll go away happy like children.’ Tory MP Adam Afriyie ‘That’s it?’ Ex-Welsh Secretary David Jones ‘Enthusiasm from Grassroots “Out” activists is in stark contrast to the scaremongering of the #Remain-ians & #ProjectFear!’ Tory MP Liam Fox Advertisement

Today’s Survation poll found that if Mr Cameron loses the referendum and is forced to resign as Prime Minister, Mr Johnson is the public’s clear first choice to succeed him, with Home Secretary Theresa May second and Chancellor George Osborne third.

A full-scale Tory war erupted over Europe at yesterday’s crisis Cabinet meeting. As the six rebels told the Prime Minister that they could not support his stance, Mr Osborne warned of economic disaster if Britain leaves the EU.

Meanwhile, Mr Cameron appealed for Ministers to avoid a public slanging match before the referendum on June 23. But when the meeting ended, the rebels left Downing Street via a rear exit and went to the London HQ of the Vote Leave campaign.

Employment Minister Priti Patel, the ‘poster girl’ of the ‘Out’ campaign, also takes a swipe at Mr Cameron’s deal in an article for today’s Mail on Sunday. She writes: ‘We should be left in no doubt that by staying in the EU, nothing will change as no significant powers or competences have been returned to Britain.’

She adds: ‘Now is the time to show the EU that the British public cannot be treated like fools. We can see through the spin, propaganda, and abuses of taxpayers’ money for endless self-serving vanity projects that are not in our democratic, economic or national interest.’ And Mr Cameron’s ‘supposed reassurances raise more questions than they answer’, she claims.

Mr Gove – Mr Cameron’s closest personal and political ally – said the EU was ‘hopelessly out of date’ and added: ‘Every day, every Minister is told, “Yes Minister, but that is against EU rules.”’

He said he was ‘pained’ to go against the PM, but added: ‘If I didn’t say what I believe I would not be true to my convictions.’

But Mr Cameron received a boost when two prominent Eurosceptic Cabinet Ministers – Business Secretary Sajid Javid and Mrs May – pledged to back his ‘In’ campaign.

Mr Javid says in an article in today’s Mail on Sunday: ‘My heart says we are better off out. My head says it’s too risky right now. I’m no Europhile, but nor am I prepared to risk undoing all that work and casting aside all the sacrifices we asked of this country [in recovering from the economic crash] while the post-Brexit talks drag on and investor confidence wavers.’

And Mrs May said: ‘The EU is far from perfect but for reasons of security, crime, terrorism and trade, it is in the national interest to remain in it.’

After yesterday’s Cabinet meeting Mr Cameron described leaving the EU as a ‘leap in the dark.’ Staying in the union would mean ‘more jobs, lower prices and greater security,’ he said.

He claimed he had got ‘the best of both worlds’ from his negotiations and Britain would be able to stay permanently out of the euro, eurozone bailouts, the EU passport-free zone, an EU Army and a federal superstate.

Neither Mr Johnson nor Mr Gove were available for comment last night.