The TV debates during next year's general election look set to end up in a '5-3-2 formation', rather than being restricted to just the three main party leaders.
Comments by David Cameron suggest he wants one debate with the three main parties alongside the Greens and Ukip, followed by another head-to-head with him and Ed Miliband.
The details will be finalised after the party conference season, but the Liberal Democrats will be angered by the prospect of being excluded from the final debate and will press for at least one to feature Nick Clegg alongside only Cameron and Miliband.
"I don't think you can have a party like Ukip without an MP if you don't have the Greens, who have got an MP," Mr Cameron told BBC Breakfast.
"I'm very keen to examine all the different formats we can have and I've suggested we can have, perhaps we should have one debate with all the parties in so that everybody can have their say and perhaps we need a debate where the two people who could actually be prime minister debate directly with each other."
Cameron is also likely to want the debates towards the start of the campaign, having spent many months complaining that the dominance of the TV debates last time derailed the entire campaign.
Labour and Liberal Democrats will fight that move and push for the debates to be closer to the end of the contest.
Regardless of the details, Cameron's comments effectively guarantee that there will be TV debates during the general election campaign. Downing Street has been retiscent to sign up to them again after many Tory MPs credited them with robbing the Tories of a majorty last time.
Labour will be jubilant at the prospect of the debates and the inclusion of Nigel Farage. They feel the Ukip leader sucks more votes from the Conservatives than he does from them - an assessment born out by polling.
Labour officials also feel Miliband excels at town hall Q&A formats, giving him an opportunity to talk over the heads of a hostile press to the public at large.
Cameron even suggested he was "pro-TV debates", opening up the possibility of a head-to-head with Nigel Farage.
The Ukip leader was quick to pour cold water on that idea.
"They are thinking about it but they won't," he said on LBC radio.
"He doesn't want to have a debate with me, of course he doesn't.
"[But] of course I want to do it."
A senior Lib Dem source said: "Both the Liberal Democrats and Labour have repeatedly said that we are ready to sign up to TV debates on the same format as last time.
"It is David Cameron and the Conservative party that have been ducking and weaving and looking for excuses not to do them.
"If the Tories are serious about TV debates, they should stop dragging their feet and get round the negotiating table."
Cameron issued a full-blooded attack on Farage today, as he intensified his criticism of the party ahead of the local and European elections.
"During this election we have seen some extraordinary statements, in many cases very,very unpleasant statements by Ukip financial backers and candidates," he said.
"I think it does go to the issue of the competence of the party - what on earth are they do selecting people and allowing people like this to be in their party?
"If they can't control what they're saying then that does raise a very big issue of competence."