The Conservatives tried desperately to put a lid on the simmering row over Europe today after Boris Johnson claimed the party could give voters a say on “key parts” of the Lisbon Treaty, even if the document has been completely ratified before the next election.

In a television interview before the start of the Conservative conference in Manchester, the Mayor of London suggested that David Cameron would still need to “give effect” to people’s views, even if the treaty was in force.

Mr Cameron has only promised a referendum on the treaty if it has not already been ratified by all 27 members of the European Union before he comes to power, and has resisted pressure to explain what he would do if the treaty had already taken effect by then.

Mr Johnson said today that he thought it was “bizarre” that people were being given no say over the prospect of Tony Blair, the former prime minister, becoming president of the EU. “I do think there should be a consultation as soon as possible,” he said, raising the prospect of a "stop Blair" referendum.

As party apparatchiks sought to play down suggestions of a split, Mr Johnson refused to discuss Europe during his set-piece address to conference, apart from a disparaging aside about Tony Blair, a potential president of the EU. Instead, the Conservative Party’s most senior elected politician appeared to draw another line between himself and the Shadow Cabinet after he was welcomed to the stage with a standing ovation. “Come on, George,” he crowed at George Osborne, the Shadow Chancellor, before imploring him to follow the model of his own economic policy in the capital.

While Mr Johnson set his own agenda, Ken Clarke, the party's most prominent Europhile, struggled to keep a lid on the row.

At a fringe event on Europe the former Chancellor repeated the official line on the matter but referred listeners to his previous comments on Europe in Hansard.

"I think the policy of the party is settled," he said. "If the treaty is ratified we will not let matters rest there. It is a settled policy with which I am content. I don't think it is sensible to change that in the middle of a conference. With my complete approval, the policy will not be changed."

He admitted, however, that his famously pro-European and anti-referendum views had not changed. "I'm not going to pretend to have had a Pauline conversion," he said.

Michael Gove, the Shadow Schools Secretary, gave a series of interviews on the subject this morning in a bid to maintain discipline on the Lisbon question, insisting the party could have only “one policy at a time”.

Mr Johnson had reignited the dispute earlier by claiming that policy would have to be reviewed once the Lisbon Treaty had been ratified.

He said: “I think there should be a referendum on this as soon as possible. I think we should do this before the process is concluded. I think it’s unbelievable Labour are trying to get away with it.”

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