Cameron and Miliband clash over TV debates

He also insisted he should be facing off against the SNP's Alex Salmond, as the former Scottish first minister would be "calling the tune" if Mr Miliband made it to Downing Street.

The exchanges came in a fiery Prime Minister's Questions session, less than two months before the nation goes to the polls on May 7.

Broadcasters have threatened to empty-chair the Premier after he dismissed proposals for two debates featuring seven party leaders and a head-to-head against Mr Miliband during the formal election campaign.

Mr Cameron had previously argued that the Greens should be included in the debates, and that they must take place before March 30. He has now indicated that he will only do a seven-way debate if it happens in the week of March 23.

Mr Miliband accused the PM of "pathetic feeble excuses", saying he should "admit the truth..he is worried he might lose again".

He insisted he would be attending the debates on the dates allocated by the broadcasters, April 2 and 16.

But Mr Cameron said: "He said any time, any place, anywhere. I told him March 23 - let's hold that debate.

"I'll tell him what has changed. We have now got a situation where it is obvious Labour cannot win without the SNP.

"He says we need the two leaders who can call the tune. That is me and Alex Salmond, so let's have the debate."

Mr Cameron said Labour was not hoping to win an outright majority any more. "They are just trying to crawl through the gates of Downing Street on the coat tails of the SNP," he said.

"What he has got to do is prove he is not a chicken and rule that out."

Mr Miliband said there was "only one person preparing for defeat and it is this Prime Minister".

"You are not going to be able to wriggle off this ...

"We know you lost to the Deputy Prime Minister last time, why don't you just cut out the feeble excuses and admit the truth: you are worried you might lose again?"

But Mr Cameron replied: "You want to talk about the future of a television programme, I want to talk about the future of the country."

The clashes came after former chairman of the BBC and ITV Lord Grade accused channel bosses of breaching impartiality rules by threatening to stage election debates without Mr Cameron.

The Tory peer said the consortium of broadcasters had been self-important, incompetent and "shambolic" during negotiations over the events.

Writing in the Times, Lord Grade - who was at the BBC between 2004 and 2006 before becoming executive chairman of ITV - insisted: "Who do the broadcasters think they are?

"Their behaviour over the election debates leads me to believe they suddenly have grossly inflated and misguided ideas of their own importance."

The peer said that "for the first time in history" the broadcasters were "unequivocally playing politics" in seeking to force the hand of elected party leaders to agree to their terms.

A Labour source said: "This shows how rattled David Cameron is over TV debates. It is a desperate move to send out a Tory peer to try to bully the broadcasters."

Meanwhile, the Guardian, the Telegraph and YouTube have said they are willing to move forward the date of their separate proposed debate by a few days to March 26 or March 27 - before the start of the so-called short campaign.

The leaders of the Conservative Party, Labour, Liberal Democrats, Ukip and the Green Party have been invited to take part.

In a letter to the leaders, the consortium wrote: "We note that the prime minister has said he is willing to take part in a debate in the week beginning March 23 and that the leader of the opposition is prepared to debate 'any time, any place, anywhere'.

"The consortium had initially proposed a date of around March 30, and an earlier date might remove one stumbling block to the debates occurring.

"We also note that the impasse in negotiations with the broadcasters means that meaningful television debates now look unlikely to take place."

Ukip leader Nigel Farage said he would participate.

"Scrutiny is an important part of democracy and for this reason I am delighted to accept the Telegraph, YouTube and Guardian invitation to this debate so that I can make the case to the British people," he said.

"I hope that the Prime Minister will muster up the courage to stand by his own words and show up to try and defend his record in government.

"Mr Cameron has failed on nearly every pledge he made to the British public in 2010 and it is evident he is afraid of butting heads with Ukip on immigration, the EU, our NHS, defence, education policy and more."

The issue of debates is set to be discussed on the floor of the House of Commons later. The Democratic Unionist Party (DUP) has triggered a discussion on the "badly managed" process to agree TV debates between party leaders ahead of May's poll.

DUP leader Nigel Dodds has insisted if the Scottish National Party (SNP) and Plaid Cymru continue to hold invites, his party should also be allowed to take part.

Mr Cameron's official spokesman confirmed that Downing Street will "look at" the revised Guardian, Telegraph and YouTube proposal for a digital debate on March 26 or 27.

Asked whether the Prime Minister could move from his "final offer" of a single 90-minute TV debate with at least seven leaders, the spokesman said: "He has held an entirely consistent view. It hasn't changed and it's not going to change."

Nearly three-quarters (71%) of voters believe broadcasters should go ahead with TV leaders' debates even if Mr Cameron refuses to take part, according to a poll. Only 13% said the debates should not take place without the Prime Minister.

Some 64% said Mr Cameron had damaged his reputation and 59% that he was behaving in a "cowardly" way by trying to avoid the debates. And 63% said that if the events take place without him, broadcasters should leave an empty lectern to mark his absence.

The ComRes survey for ITV News found that Mr Cameron is the only party leader to be believed by a majority of voters (64%) not to want the debates to take place. Only 15% of those questioned said they thought the Prime Minister wants them to go ahead, against 72% for Mr Miliband, 71% for Mr Farage, 63% for Deputy Prime Minister Nick Clegg and 58% for Green leader Natalie Bennett.

But voters think that, if he does take part, Mr Cameron will out-perform all his rivals except Mr Farage. The Ukip leader was rated most likely to "win" the debate by 32% of those questioned, followed by the Prime Minister on 27%, Mr Miliband on 24%, Mr Clegg on 11% and Ms Bennett on 5%.

Answering questions at the Retail Week Live conference in London, former Labour strategist Lord Mandelson said broadcasters were not entitled to "empty-chair" leaders who refuse to take part in debates.

The former business secretary said: "I think voters feel entitled to have that sort of debate and comparison directly in front of them.

"I think that David Cameron, though, is entitled not to do that debate in the particular way the broadcasters have prescribed and the Labour Party is entitled to make him look and appear completely 'frit' and chicken and force him to take a hit for not doing the debates.

"What I don't think is that the broadcasters then are entitled to impose what they want on the political parties and empty-chair party leaders.

"I don't think the broadcasters have that entitlement. They are broadcasters, they are not the House of Commons. Who elected them?"