Boris Johnson, pictured at a homeless charity, has reportedly told Tory MPs he does not want to run the Leave campaign at the EU referendum

Boris Johnson has told eurosceptic MPs he will not lead the Leave campaign at the EU referendum - claiming 'I am not an 'outer''.

The London Mayor - who just last week insisted Britain could have a great future outside the EU - reportedly held talks on the issue before Christmas.

Mr Johnson has kept his views on Europe vague sometimes appearing more eurosceptic than on other occasions.

Today's report will come as a blow to Leave campaign organisers seeking a big name to front their challenge.

Prime Minister David Cameron is widely expected to spearhead the campaign to keep Britain inside the EU once his renegotiation is finished.

That is due in February - meaning the referendum could be held as soon as June.

Mr Johnson is said to have told the Tory backbenchers: 'The trouble is, I am not an 'outer'.'

The new remarks will fuel speculation Home Secretary Theresa May could seize the chance to be the face of the Leave campaign.

Mr Johnson was seen as hedging his bets last week, insisting while David Cameron was doing a ‘brilliant job’, Britain must be ‘prepared to walk away’ if the deal he secures is not good enough.

His remarks – dubbed ‘classic Boris’ by one Government aide – kept his options firmly open for potentially leading the Leave campaign.

Last week he told the BBC Britain could have a 'great future' outside the EU and refused to rule out campaigning against the Prime Minister when the referendum is called.

Mr Johnson said: 'My own view is I want to be part of a reformed EU, I've always said that - but if we can't get the reform we need then Britain has a great future outside in a different relationship.'

Mr Johnson said he was awaiting the outcome of the negotiations, but asked if he could campaign against Mr Cameron, the London Mayor said: 'Let's see what happens... let's see where we get to.

'It is important in these talks to be robust.'

The new remarks, reported by the Daily Express, come after Lord Tebbit, writing for The Mail on Sunday, said the ‘Out’ campaign is ‘crying out for inspirational leadership’. Riven with splits, it currently ‘lacks the muscle to carry the day’, the peer argues.

He calls on high-profile Eurosceptic Cabinet Ministers to step forward once the Prime Minister has completed his renegotiations, saying: ‘Those who claim to believe in Britain need to lead Britain.’

Charismatic Mr Johnson has been the subject of a political tug of war, as Tories from both the ‘In’ and ‘Out’ camps battle to win his approval.

There has been speculation that Downing Street could secure Mr Johnson’s support by adopting one of his flagship pre-referendum demands. He has called for MPs to be given the power to apply an emergency ‘brake’ on EU laws in exceptional circumstances.

This would require an amendment to the 1972 European Communities Act to say Britain has complete sovereignty over its legal system.

The idea was dismissed by No 10 when Mr Johnson first floated it last year – but Government legal experts are understood to be taking a fresh look. A friend of the Mayor of London said: ‘It would not be the first Boris brainwave Dave has ended up backing. The Germans already do something very similar.’

Some officials say the idea is ‘purely symbolic’ because Parliament can already ignore legally flawed directives. ‘It would be legally unnecessary but could be done as political theatre or sabre rattling,’ said one.

Head to head? Mr Johnson ruling himself out of the running to head the Leave campaign could create an opportunity for Theresa May, right, to campaign against David Cameron, pictured left leaving Downing Street today, at the referendum expected later this year

A Downing Street spokesman said it was ‘not giving a running commentary on the issue’.

Mr Johnson was at the centre of further rumours after he was overheard telling fellow Eurosceptic Mr Javid in a Commons corridor last week: ‘Perhaps you and I should join forces.’ But sources denied it was part of an anti-EU plot, saying the comment was ‘light-hearted’.

After a bright start, the ‘Out’ campaign has been dogged by internal squabbles, with three separate organisations and a failure to land a high-profile figurehead.

Commons Leader Chris Grayling and fellow Ministers Iain Duncan Smith and Theresa Villiers have made it clear they will back the campaign to quit the EU. But a senior ‘Out’ camp source said they lacked ‘star quality’.

‘If Boris and Theresa May back us it would be a game-changer,’ said a prominent Eurosceptic campaigner. ‘Without someone like that, it will be tough. Nigel Farage has lost credibility, and Grayling and Duncan Smith are worthy and well-meaning but not box office.

‘Against the megabucks juggernaut of Brussels and the No 10 machine we will struggle.’

Most opinion polls show support for Britain leaving the EU is stubbornly short of 50 per cent.

Lord Tebbit also warned that any would-be future Tory leader could pay a heavy price for failing to support the ‘Out’ campaign.