The Liberal Democrat leader said he was still hopeful the events would take place, insisting Mr Cameron should “swallow his pride” and agree to take part.
But Chancellor George Osborne has defended the PM’s position, arguing that the proposed format is not fair because it includes Ukip but not the Green Party. The Greens believe their membership overtook that of Nigel Farage’s party overnight thanks to a 1,800-strong surge.
Mr Cameron endured a torrid time in the Commons yesterday as Ed Miliband accused him of being “frit”.
Broadcasters have proposed three debates - one head to head between Mr Cameron and the Labour leader, another also involving Mr Clegg, and a third with Mr Farage thrown into the mix.
But the PM has suggested there should only be two sessions - one where he takes on Mr Miliband alone, and another where they are joined by all the “minor parties”.
Speaking on his regular LBC phone-in, Mr Clegg said Mr Cameron was coming up with “one excuse after the next” and questioned why he was concerned about the Greens rather than Plaid Cymru or the SNP.
“At the end of the day, the point that I’d be making to David Cameron - and he’d save himself a lot of anguish over the weeks and months because people are going to continue to mock the way he is running away from all this - is just to accept the basic principle it’s not up to him or to me or to Ed Miliband or anybody to decide how these debates finally take place,” he said.
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“It is for the broadcasters to put forward proposals, they’ve put forward proposals. As it happens I am not totally happy with the proposals they have put forward but everyone’s going to have to swallow their pride and put the interest of the British people, who want these debates to take place, first.”
Asked whether he thought the debates would take place, Mr Clegg said: “I really hope they will ... I think they will, because I think David Cameron has put himself in an unsustainable and actually slightly laughable position, and you could feel it in the House of Commons yesterday - the idea that suddenly this heartfelt concern about one Green MP - it’s such a see-through excuse, wafer thin ...
“If he rules himself out of it, then he rules himself out of it. I really do hope the broadcasters develop a bit of backbone on this, because they shouldn’t be bullied by the Conservatives throwing their weight around.
“It would be much better if he was there. I rather enjoyed debating him last time. I thought I did rather well.”
The Green Party said that it had picked up 1,800 members since yesterday afternoon, and believed it had overtaken Ukip.
The party now has 43,361 members across its organisations in England and Wales, Scotland, and Northern Ireland. As of yesterday Ukip had 41,943.
A spokesman said the figures undermined Ofcom’s view that the Greens should not be classed as a major party for the purposes of coverage in the election campaign. “The ongoing membership surge and latest polling further calls into question the idea that we are not a major party,” the spokesman said.
Interviewed on ITV’s Good Morning Britain, Mr Osborne said the broadcasters had got it wrong.
“David Cameron wants to take part in the TV debates, he has taken part in them before,” he said.
“He has said very clearly the Green Party should be involved if you’ve got all the parties. He’s made it pretty clear that that is what he’d like to see. It’s only fair.
“He wants to get the format right. I think most people watching this say ‘We’ll either watch all the parties taking part in this debate, or let’s have a head-to-head between the two people who could be Prime Minister, David Cameron and Ed Miliband’.
“The broadcasters, they seem to have come up with neither of those plans. We’re just saying come up with a good plan, of course we want to take part.
“There would never have been TV debates in this country if it hadn’t been for David Cameron last time saying ‘I will take part’.
“In the past, when someone looked like winning an election, they’ve said no. David Cameron last time said yes.
“We’re up for the debate but let’s have the right plan.”
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