David Cameron rejected calls to promise a referendum on the Lisbon treaty even if it had been ratified, as he struggled yesterday to maintain a united front on the issue.

Boris Johnson, the Mayor of London, denied that there was a rift between him and Mr Cameron after he had appeared to demand a referendum come what may, to prevent the prospect of Tony Blair becoming president of Europe. Eric Pickles, the Conservative Party chairman, spoke with surprising confidence of Britain being able to hold a referendum because the treaty would not have been ratified before the general election. He suggested that the Czech Republic would not ratify for several months.

After Saturday’s “yes” vote in the Irish referendum on the treaty, the Tory leader was under pressure to explain what he would do if it had been implemented by the time a Conservative government came to power.

He insisted yesterday morning that he did not want to speculate as long as the two remaining member states — Poland and the Czech Republic — had yet to ratify. “I don’t want to say anything or do anything now that would undermine or prejudice what is happening in other countries, where they are still debating whether to ratify this treaty,” he told The Andrew Marr Show on BBC One.

“There were three countries that it hadn’t been ratified in — Ireland, the Czech Republic and Poland. I don’t see any reason to change our approach because one of those has decided to ratify. I think people will understand this argument that while there are countries delaying the implementation of this treaty, don’t do anything or say anything that stops them from doing that.” Mr Cameron had told friends that he was determined to keep open the Tory stance, to encourage the Czechs to hold out.

But later yesterday President Klaus of the Czech Republic warned Mr Cameron that it was now “too late” for the treaty to be stopped, and President Kaczynski of Poland indicated that, after Ireland’s vote, he would sign “without due delay”.

Mr Johnson told The Sunday Times that the prospect of Mr Blair becoming the new EU president under the terms of the treaty underlined the need for a referendum, even if it had been ratified. “If we are faced with the prospect of Tony Blair suddenly emerging, suddenly pupating into an intergalactic spokesman for Europe, then I think the British people deserve a say,” he said. “I do think it would be right for such a debate to be held, particularly if the upshot of the Lisbon treaty is going to produce President Blair.”

David Miliband, the Foreign Secretary, said: “Boris Johnson’s comments show that the Tories are split right to the top on Europe.”

A spokesman for Mr Johnson played down talk of a rift. He said: “Boris Johnson was expressing the deep frustration felt by every Conservative and most voters that the Government has agreed to surrender significant powers to the European Union without allowing voters a say in a referendum.

“There is no rift with David Cameron and his position does not conflict with that of the party leadership.”

The Eurosceptic Tory backbencher Richard Shepherd said that the party ought to go ahead with a referendum regardless of whether the treaty was in force. “We were committed to it and I believe that this is a matter of the deepest trust with the British people that we will honour that which we gave the commitment for,” he told The World This Weekend on BBC Radio 4.

But the former European Commissioner and Conservative Cabinet minister Lord Brittan of Spennithorne said that it would be ludicrous to try to unpick a treaty that had already been implemented. “I can’t believe that a Conservative Party would, in government, want to have a referendum if the treaty is in force. I am sure wiser counsels will prevail,” he said.

“To have a referendum asking Europe to unravel what is already in force would be not just politically unwise but ludicrous and impossible.”

William Hague, the Shadow Foreign Secretary, said that if the treaty were ratified by Poland and the Czech Republic, the party would set out its position at that point. “We will, whenever that happens, if that happens, set out how we intend to proceed. We won’t wait for the general election to do that, we will be very straightforward with people,” he told The World This Weekend.

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