Boris Johnson says David Cameron hasn't yet convinced him to support staying in the EU

Boris Johnson has said he has not yet decided whether to support David Cameron’s campaign for Britain to remain in the European Union.

The Mayor of London – a possible successor to the Prime Minister – held talks at Downing Street with Mr Cameron to discuss his position on the issue.

Emerging from Downing Street he reportedly said that nothing had changed in his position.

The delay in whether to back the PM’s renegotiated position comes as Mr Cameron is locked in negotiations with European leaders over the nature of a deal to change Britain’s membership of the EU.

After that deal is secured the PM plans to hold and in-out referendum on Britain’s membership of the bloc – possibly as early as June this year.

But Mr Cameron was told yesterday by eastern European countries including Poland that a draft plan to restrict EU migrants from claiming in-work benefits would not fly, however.

Emerging from Downing Street after the talks, Mr Johnson told reporters: “I’ll be back – no deal as far as I know.”

Sources close to the Mayor say he will make his position clear after the EU summit to determine the reforms to the bloc.

Mr Johnson is one of a number of favoured successors to Mr Cameron, who has said he will step down before the next election.

Other contenders include the Home Secretary Theresa May, former defence secretary Liam Fox, and the Chancellor George Osborne.

The Mayor has characteristically blown hot-and-cold on the EU issue in recent years, making statements that are sometimes interpreted as eurosceptic but also shying away from backing exit.

At the weekend he said Britain should not be “afraid” of Brexit and last month he said Britain could have a “great future” outside the European Union.

Last year he said he could vote to leave the EU but would wait to see how Mr Cameron’s negotiations went.

A draft deal drawn up by European Council president Donald Tusk was hail by Mr Cameron as a victory in his negotiations – but the deal’s proposals on restricting EU migrant benefits appeared to not go as far as previously suggested.

Polls suggest the deal has been rejected by the public, most of whom believe it is a “bad deal for Britain”. Leading eurosceptics in Mr Cameron’s own party have described the plan as “thin gruel” and “watered down”.

Despite the lack of enthusiasm for the plan at home Mr Cameron however faces and uphill struggle to get countries with large numbers of EU nationals coming to the UK to agree to it.

He will attend a further summit in Brussels on Friday where he will discuss the situation with EU leaders.