Conservative ministers should be allowed to campaign to leave the EU and keep their jobs, Boris Johnson said today.

The London Mayor reopened the row over whether David Cameron would sack ministers who did not back him in the in-out referendum, after the Prime Minister was forced to claim his threat had been 'misinterpreted'.

Mr Johnson said it would be 'safer and more harmonious' to let Eurosceptic ministers stay in the government than attempt to 'bind everybody in' to voting to stay in the EU.

Scroll down for video

London Mayor Boris Johnson today said ministers should be allowed to keep their jobs while campaigning for Britain to leave the European Union

Mr Cameron has pledged to renegotiate Britain's membership of the EU before staging an in-out referendum by 2017, and possibly as early as next May.

If the Prime Minister gets the deal he wants, he will recommend that Britain votes to stay in the EU.

But senior ministers who want to leave the EU hope to remain in the government while campaigning for Brexit.

Mr Cameron will be in the Commons today to see the introduction of the EU Referendum Bill, paving the way for an in-out vote to be held before the end of 2017.

But what should have been moment of triumph for the Prime Minister has been dogged by chaos and confusion over whether ministers in his government will be free to campaign to leave the EU.

On Sunday Mr Cameron said that rebels would be ordered to toe the line in the vote on Britain’s membership of the EU.

But amid a furious backlash from Tory MPs, yesterday he insisted he only demanded loyalty during his renegotiation of Britain's membership of the EU.

Now Mr Johnson has broken cover to suggest the only way to stop the Tories tearing themselves apart over Europe is to allow ministers to remain in post while campaigning for Brexit.

I think probably it would be safer and more harmonious just to say "OK you make your minds up"

He told LBC: 'I think in 1975 from memory I think Cabinet ministers were allowed to campaign against staying in and to keep their positions. I don’t see why not myself.

'Just thinking about it out loud on the spur of the moment let me think: I think probably it would be safer and more harmonious just to say "OK you make your minds up".

'I think probably on something like this, do you really need to bind everybody in? There will be different views, get it over.

'The prime minister will be able to make a recommendation. It’s almost certain if he gets the deal that he wants the overwhelming majority of his colleagues on both the front and backbenches will support him.'

Mr Johnson told LBC's Nick Ferrari said it would be 'safer and more harmonious' to let Eurosceptic ministers stay in the government than attempt to 'bind everybody in' to voting to stay in the EU

HOW CAMERON LAID DOWN THE LAW... AND THEN RETREATED Sunday 1pm: David Cameron tells reporters at the G7 Summit that ministers will have to toe the line during the referendum campaign. Asked whether they will have to quit in order to campaign for Britain to leave the EU, he replies: ‘If you want to be part of the Government, you have to take the view that we are engaged in an exercise of renegotiation to have a referendum, and that will lead to a successful outcome.’ 10pm: The front pages of the next day’s newspapers appear on the Internet. The Daily Mail, Guardian, Daily Telegraph, Times, Express and Financial Times all report Mr Cameron’s threat to dismiss rebel ministers. Downing Street makes no complaint. Yesterday 7.50am: Communities minister James Wharton is sent on to BBC Radio Four to defend the position. Asked if rebel ministers will have to quit, he says: ‘That is, fundamentally, what that means.’ 11am: The Prime Minister’s official spokesman uses her daily briefing to complain that Mr Cameron’s remarks have been ‘over-interpreted’. 2.45pm: The issue dominates the Prime Minister’s closing press conference at the G7. He accuses reporters of ‘misinterpreting’ his comments. 6pm: Rebel Tories welcome the change of heart. Tory grandee David Davis says: ‘It’s a welcome reinterpretation.’ Advertisement

Mr Cameron has pledged to renegotiate Britain's membership of the EU before staging an in-out referendum by 2017, and possibly as early as next May.

Senior ministers who want to leave the EU hope to remain in the government while campaigning for Brexit.

On Sunday Mr Cameron briefed reporters at the G7 summit in Bavaria, and appeared to repeat an earlier insistence that all ministers must toe the government line.

With most newspapers and the BBC reporting his threat, Tory minister James Wharton went on the radio at 7.50am yesterday to defend the idea that the Cabinet must vote in the same way.

But by 11.15am Downing Street was in reverse, insisting the Prime Minister was only demanding ministers support his renegotiation plans.

And then at 3.30pm Mr Cameron tried to clear up the confusion, claiming: 'It is clear to me that what I said yesterday was misinterpreted. I was clearly referring to the process of renegotiation.

'But the point is this. I have always said what I want is an outcome for Britain that keeps us in a reformed EU. But I have also said we don't know the outcome of these negotiations, which is why I have always said I rule nothing out.

'Therefore it would be wrong to answer hypothetical questions. I know that can be frustrating. I know you want to jump to the end of the process and have all the questions answered now about the end of that process.

'That is not going to be possible. You are going to have to take this stage by stage, step by step and you will get the answers.'

But the remarks will do little to quell the sense of chaos over the government's policy, with Number 10 buffeted by Tory Eurosceptics furious at the idea that ministers would be forced out of office to campaign to leave the EU.

David Cameron’s was forced to shelve a threat to sack ministers if they campaign to leave the EU

A Downing Street transcript clearly showed Mr Cameron’s comments on Sunday came in answer to questions about whether ministers would have to quit to campaign for Britain to leave the EU during the referendum.

In reply he said: ‘I’ve been very clear, which is I’ve said that if you want to be part of the Government, you have to take the view that we are engaged in an exercise of renegotiation to have a referendum, and that will lead to a successful outcome.’

Senior Tories condemned the idea that ministers would be forced to toe the line on a question as contentious as Britain’s membership of the EU.

Graham Brady, chairman of the powerful backbench Tory 1922 Committee, said that MPs should be given space to express ‘deeply held convictions’.

‘It is generally better to work with the grain, to engage colleagues, than to try to force them into places where they cannot go,’ he told Total Politics magazine.

Mr Mitchell, who cut his teeth as a whip during the fraught Maastricht Treaty votes in the mid-1990s, said: ‘My strong advice to the Prime Minister would be to let ministers campaign and vote as their conscience and their convictions dictate. Not to do so will put too much pressure on the parliamentary party and the lid could blow off.’