David Cameron should allow Government ministers to campaign for a British exit from the European Union in the promised referendum even if he recommends staying in, Boris Johnson has said.
The mayor of London, a member of the Prime Minister's political Cabinet, said it would "probably be safer and more harmonious" for Mr Cameron to allow ministers to campaign on the opposing side.
Mr Johnson's comments, on the day legislation for the referendum faced its first Commons challenge, reopened a row over whether the Prime Minister would sack ministers who campaign to leave the EU.
Attending a G7 summit in Germany, Mr Cameron sought to blame the media for "misinterpreting" his position - insisting he will not announce until nearer the time of the public vote whether senior colleagues will be bound by collective responsibility.
Mr Johnson said that, at the time of the last referendum in 1975, then-prime minister Harold Wilson allowed ministers to speak on opposing sides and "it seemed to work back then".
Asked if ministers should be allowed to campaign for "Brexit" and keep their posts, Mr Johnson said: "I don't see why not myself."
In a reference to the confusion over Mr Cameron's comments in Germany, he told LBC Radio: "We seem to have been around the houses a bit on this.
"I think, probably, it would be safer and more harmonious just to say 'OK, you make your minds up'. I think, on something like this, do you really need to bind everybody in?"
He said that if Mr Cameron got the deal he wanted in Europe, "the overwhelming majority of his colleagues - on both the front and the back benches - will support him".
Mr Johnson left the door open to campaigning for Brexit if the Prime Minister did not achieve an acceptable deal, saying "Let's see where we get to"