David Cameron has paved the way for a televised showdown with the Ukip leader Nigel Farage in the run-up to next year’s general election.
He signalled his support for a five-way debate with the leaders of all the main parties, as well as a separate head-to-head confrontation with Ed Miliband, the Labour leader.
The other parties have accused Mr Cameron of trying to stall discussions over the format of debates in an attempt to avoid an appearance.
The Tories have said talks on the issue should not take place until after the party conferences in October.
Many Conservatives are still scarred by the three televised debates of the 2010 campaign, some arguing that his performance was a factor in failing to secure an overall Commons majority.
The party would also be wary of pitting the Prime Minister against Mr Farage, whose populist style has helped Ukip to pick up widespread support from disillusioned Tory voters.
But Mr Cameron insisted he was not opposed to the principle of pre-election debates as long as the parties and broadcasters could reach agreement on their format.
He raised the prospect of one session bringing him together with Mr Miliband, Mr Farage, Nick Clegg, the Liberal Democrat leader, and Natalie Bennett, the Green Party leader.
He said: “I have suggested perhaps we should have one debate with all of the parties and so everyone can have their say, and perhaps we need a debate where the two people who could be Prime Minister debate directly with each other.
“You can have a debate where you have all of the parties. I don't think we could have a party like Ukip without an MP if you don’t have a party like the Greens, who have an MP.”
It was reported last week that Mr Cameron favoured three debates in a “two-three-five” format: encounters between him and Mr Miliband; between him, Mr Miliband and Mr Clegg; and between the five leaders.
He told the BBC he believed some of the debates should take place before the formal launch of the election campaign and added: “There are still a number of issues that have to be ironed out. But I helped make the debates happen last time. I’m pro-TV debates.”
But Mr Farage, who was widely judged to have “won” two recent televised debates with Mr Clegg on the European Union, claimed the Tory leader would ultimately duck the confrontation. He said Mr Cameron would not want to discuss immigration or Europe with him.
“They are thinking about it and they won't say anything until after the party conference season in October and then they will decide it’s not a very good idea,” the Ukip leader said.
Labour and the Liberal Democrats accused Mr Cameron of trying to dodge talks over the debates.
Michael Dugher, the shadow Cabinet Office Minister, said: “If he is serious about this, he should stop dithering, appoint his negotiators and get on with it.
“It’s nonsensical for Cameron to say he wants to start the debates early, but the negotiations late.”
A senior Lib Dem source said: “If the Tories are serious about TV debates, they should stop dragging their feet and get round the negotiating table.”