Boris Johnson says EU referendum would be a 'good idea'
Boris Johnson has suggested a referendum on Europe would be a "good idea", potentially putting himself at odds with David Cameron over the issue.
The Mayor of London said the British people had not been directly consulted on Europe since 1975 and he would be "very, very interested" in the outcome.
But his spokesman later insisted the comments were purely "hypothetical".
The prime minister has said a so-called in-out referendum would be the "wrong answer" for the country.
The government have said the public must be consulted on any future substantial transfer of sovereignty from the UK to the EU but have distanced themselves from any poll in the foreseeable future.
Many Conservative MPs want a vote now on whether to stay in the EU and the Commons is set to debate the issue later this year.
However few have spoken out publicly about the issue during the conference, which ends on Wednesday, after warnings the party must not appear obsessed with it.
Asked about the matter at a fringe event organised by London's LBC radio, Mr Johnson raised the possibility of some form of referendum on the UK's relationship with the EU.
"The British people haven't had a say on Europe since 1975," he said.
"There hasn't been a vote. If a reasonable question could be framed and put to the people of this country it is not a bad idea."
The Mayor of London, who is standing for re-election next year, said the outcome of any vote was "far from a foregone conclusion".
"I think if you had an in-out referendum, I would be very, very interested (in the outcome).
"I wouldn't be at all surprised if the British people, having really thrashed the arguments out, might decide that voting to come out was not the answer but what they wanted was some looser relationship.
"They might want to re-negotiate the package, they might want to get rid of some competencies of Brussels."
Mr Johnson later issued a statement saying he was merely speculating on a "hypothetical question".
His spokesman said he did not believe "a referendum at this point would serve any useful purpose".
The London mayor told the BBC: "I strongly support David Cameron.
"His decision not to raise Europe up on the political agenda is absolutely right. It is right to focus on the economy at this time"
David Cameron has said exiting the EU would harm the UK's economy and that policymakers should focus on resolving Europe's current economic problems - suggesting his views are shared by most people in the country.
However, he has stressed this should not stop the UK from pressing for change within the EU and he has held out the possibility of UK clawing back some powers in the future.
Separately, Mr Johnson has ruled out standing for election as an MP while he remains mayor of London.
Despite media reports he wants to lead the party, there was "not a snowball's chance in Hades" he would stand for Parliament if Londoners re-elected him next year, he told BBC Two's Newsnight.
Mr Johnson, who was an MP before becoming Mayor, has been tipped as a successor to David Cameron but he added: "I don't think I will do another big job in politics after [being mayor]."