Lord Pearson said he was "so angry" with the Conservatives
The UK Independence Party says it offered not to fight the next general election if the Conservatives agreed to hold a referendum on the Lisbon Treaty.
New UKIP leader Lord Pearson of Rannoch told the Times he offered a deal after its strong European elections showing.
He told the BBC he thought a referendum would have gone against the treaty - meaning Britain would have effectively left the EU and UKIP could disband.
The Conservatives said any mention of a deal had been rejected "straight away".
Lord Pearson was chosen as UKIP's new leader on Friday, replacing Nigel Farage, who stood down to focus on running for Parliament at the next general election.
The ex-Tory peer told the BBC: "Well, the version in the Times is slightly paraphrased and condensed.
"We offered that if we got a clear, written promise with an agreed wording for a referendum on whether we stayed in or left the European Union... then we would stand down for the general election, providing we had this absolutely clearly in writing.
"And then when we had the referendum - which we believed we would win - we would then be out of the European Union and then at that point UKIP, well it would have been up to UKIP, but it would probably have disbanded because its major point would no longer be in existence."
Lord Pearson said he had taken the proposed deal to Lord Strathclyde, the Conservative leader in the Lords, after UKIP beat Labour into third place in this year's European elections.
He said he was acting on behalf of Mr Farage and told Lord Strathclyde to relay the offer to Tory leader David Cameron.
Lord Pearson told the BBC: "We made this offer to Tom Strathclyde, who was going to see David Cameron two days later. He said I'll talk to David."
However Lord Pearson said in the end he did not get an answer. He told the Times: "I'm so angry with them now."
The Times said both Mr Farage and Lord Strathclyde had confirmed the meeting did take place.
Earlier this month, the Conservatives said ratification of the Lisbon Treaty by the Czech Republic - the last EU country to do so - meant their campaign for a referendum had come to an end.
The decision prompted UKIP, as well as Eurosceptics in Mr Cameron's own party, to accuse him of reneging on a "cast-iron" guarantee made in 2007 to hold a vote.
But Mr Cameron said that to press ahead with a referendum post-ratification would be "simply to have one for the sake of it".
Shadow Europe minister Mark Francois said of Lord Pearson's comments: "We don't make policy on the basis of secret deals with other parties; we decide our policies on the basis of what is right for the country.
"As we have said, a made-up referendum after ratification would be pointless."
Lord Pearson gained nearly half of the approximately 9,900 votes cast by UKIP members in the leadership contest.
Following his victory, he said the Lisbon Treaty was "the last nail in the coffin of our democracy" and his objective at the next election would be to force a hung Parliament and a "realignment" in British politics.
UKIP does not have any MPs but has 13 MEPs and among its key aims is pulling the UK out of the European Union.