David Cameron is trying to avert a row over the Lisbon Treaty
Tory Euro MP Daniel Hannan has said David Cameron is "working privately to get a referendum on the Lisbon Treaty".
The Tory leader has said he does not want to prejudice debate in countries who have yet to ratify the Treaty.
However his office admitted Mr Cameron had written to the president of one of those countries - the Czech Republic - setting out his opinion on the Treaty.
A Yes vote on the Treaty in Ireland has ensured it has dominated the eve of the party's conference in Manchester.
It also re-ignited Tory opposition to former Prime Minister Tony Blair becoming the European Union's first president.
Mr Cameron has pledged to hold a referendum on the Treaty in the UK if it has not been ratified, should the Conservatives win the next general election, which is widely expected to be in May.
He has so far declined to say what the Conservatives would do if the Treaty has been ratified - and he is under pressure from the Eurosceptic wing of his party to hold a referendum no matter what.
One Eurosceptic backbencher, Richard Shepherd, said he believed the party was "committed to it".
Mr Cameron has attempted to calm a potential revolt by saying there will be no new announcements on the Lisbon Treaty during the conference, which will be the last before an election.
He told BBC One's Andrew Marr show he will not publicly commit to a post-ratification referendum because he did not want to interfere in the debate in Poland and the Czech Republic - the two countries who have yet to ratify the Treaty.
However, in a hand-written "private" letter to Czech President Vaclav Klaus before the Irish vote, he restated his opposition to it.
Mr Cameron told Andrew Marr: "I don't want to prejudice the rest of Europe. It's not been ratified in two countries so I'm not going to change our approach now one of those three has been ratified."
But MEP Daniel Hannan, who wants British withdrawal from the EU, suggested Mr Cameron was working behind the scenes to ensure there would be a UK referendum.
Asked if Mr Cameron was working with the Czechs and Poles, Mr Hannan said the Tory leader is not "just going through the motions, he is absolutely committed to a referendum".
Mr Hannan also said that the party leadership had not ruled out a broader referendum on Britain's relationship with the European Union.
On the issue of the new role of president, which will be created by Lisbon Treaty ratification, Foreign Secretary David Miliband told Sky News Tony Blair would be an "excellent choice" for it and accused the Tories of "silly partisanship" in trying to block him.
London Mayor Boris Johnson earlier told The Sunday Times that the prospect of the former prime minister becoming the new EU president under the terms of the Lisbon 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."
Mr Blair's hopes of taking on the high profile new role received a boost with Irish Prime Minister Brian Cowen declaring that he would be "very supportive" if he were to put his name forward.
But shadow foreign secretary William Hague has warned that the Tories would be prepared to lobby European capitals to block Mr Blair's appointment.
David Miliband said Boris Johnson's comments show the "Tories are split right to the top on Europe" - something later denied by Mr Johnson's spokesman.
Mr Miliband also refused to apologise for saying he was "sickened" by the Tories' alliance with Latvia's For Fatherland and Freedom party and insisted he was right to personally criticise Tory chairman Eric Pickles.
Mr Pickles has repeatedly demanded an apology for an "indecent" accusation in Mr Miliband's speech to Labour's conference last week that Mr Pickles effectively defended the Waffen SS by claiming their members were only "following orders".
Mr Miliband refused to back down in a clash with Mr Pickles on BBC One's Politics Show, saying the Tories were in league with politicians they "wouldn't be seen dead with" in the UK.