Media playback is unsupported on your device Media caption Ed Miliband accuses David Cameron of "pathetic and feeble excuses" but is told he is "despicable and weak"

Ed Miliband and David Cameron launched attacks on each other's character in angry Commons exchanges over televised election debates.

The Labour leader accused the PM of "chickening out" of a debate with him, saying: "Like all bullies, when the heat is really on he runs for cover."

Mr Cameron attacked Mr Miliband as "despicable and weak" for not ruling out a post-election deal with the SNP.

It came amid a fresh effort to break the TV debate deadlock.

YouTube, the Guardian and the Daily Telegraph have offered to bring forward the proposed date of an online debate - which would include the leaders of the Conservatives, Labour, Lib Dems, UKIP and the Greens - to either 26 or 27 March, in an effort to meet the prime minister's demands any debate happens before the official campaign begins on 30 March.

Downing Street has said it will "look at" the proposals.

'Wriggle off'

The issue dominated Prime Minister's Questions - the last but two before polling day - with the Labour and Conservative leaders in full electioneering mode, battling deafening noise from MPs.

Mr Miliband said the PM's handling of the election debate issue "goes to his character", telling him: "The public will see through your feeble excuses.

"Instead of these ridiculous tactics, why don't you show a bit more backbone and turn up for the head-to-head debate with me? Any time, anywhere, any place."

Media playback is unsupported on your device Media caption Robin Brant explains why empty chairs and chicken noises have become part of the row.

Mr Cameron claimed Mr Miliband was "despicable" for trying to "crawl into Downing Street" in alliance "with people who want to break up our country".

He challenged the Labour leader to reject a post-election deal with the SNP, adding that if "he had an ounce of courage he would rule it out".

Mr Miliband hit back, saying Mr Cameron would not be able to "wriggle off" the debates and said "there is only one person preparing for defeat and it is this prime minister".

"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?"

'Call the tune'

Mr Cameron replied: "You want to talk about the future of a television programme, I want to talk about the future of the country. Four questions, three weeks to go, you can't talk about jobs because we are growing jobs. You can't talk unemployment, because unemployment is plummeting. You can't talk about inflation because it is at a record low.

"The truth is you are weak and despicable and want to crawl to power in Alex Salmond's pocket."

He said the head-to-head debate should be between the two people who "actually call the tune - that is me and Alex Salmond".

Mr Miliband has repeatedly rejected calls, including from some of his own MPs, to rule out a post-election deal with the SNP.

A source close to the Labour leader said: "Our position is unchanged. The only way to get a Labour government is to vote Labour and we will leave it to others to talk about post-election scenarios.

The SNP's leader at Westminster, Angus Robertson, predicted Labour would have to do a deal with the SNP.

"There is an offer on the table," he said.

"If the numbers are such that the Labour Party cannot command a majority they will have to work with the SNP."

Image caption Lord Grade said broadcasters should "get back in their box"

Although neither leader referred to the digital debates option in the Commons, Conservative Party chairman Grant Shapps told the BBC's Daily Politics that seemed a "plausible" way forward.

'Courage'

UKIP leader Nigel Farage said: "Scrutiny is an important part of democracy, and for this reason I am delighted to accept the Telegraph/Guardian/YouTube invitation to this debate - so that I can make the case to the British electorate on why they should vote UKIP.

"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."

Lib Dem general election co-ordinator Lord Ashdown said the party remained committed to election debates and would consider the digital debate proposal.

But he said the prime minister should not be able to let it excuse him from taking part in the equivalent TV debates.

Labour has yet to respond to the digital debate offer.

The proposal is for a five-way debate, which would include UKIP and the Greens.

A Green Party spokesman said the party was "looking forward to receiving the invitation from the Guardian/YouTube and Telegraph" and would "relish" the chance to take part.

Planned debate schedule

2 April: Seven-way debate featuring David Cameron, Ed Miliband, Nick Clegg, Nigel Farage, Nicola Sturgeon, Natalie Bennett and Leanne Wood (ITV broadcast)

16 April: Seven-way debate featuring David Cameron, Ed Miliband, Nick Clegg, Nigel Farage, Nicola Sturgeon, Natalie Bennett and Leanne Wood (BBC broadcast)

30 April: Head-to-head debate featuring David Cameron and Ed Miliband (Channel 4 and Sky News broadcast)

The BBC, Sky, ITV and Channel 4 plan to hold three live televised debates in April - two featuring the leaders of Conservatives, Labour, the Liberal Democrats, the SNP, Plaid Cymru, UKIP and the Green Party, then one with only Mr Cameron and Labour leader Ed Miliband.

But they face a threat from the Democratic Unionist Party (DUP), which is angry at being excluded and is calling for an independent body to be put in charge of television election debates in a Commons debate on Wednesday.

And last week Mr Cameron said his "final offer" was to take part in a single debate of seven party leaders before 30 March - an offer which was rebuffed by the broadcasters who said they would go ahead with their three planned debates with or without him.

That stance came under fire on Wednesday morning from former BBC, ITV and Channel 4 boss Lord Grade, who suggested broadcasters were breaching impartiality rules and "playing politics".

The Conservative peer said it was "not acceptable for unelected journalists" to replace David Cameron with an "empty chair" if he refused to take part in any televised debates.

In a joint response to Lord Grade's comments, the broadcasters said they were "trying to deliver debates because we know our audiences want them".

"In 2010 they were watched by more than 20 million people and our research suggests there is an appetite for them in 2015. We have issued invitations to seven party leaders and we continue to hope they will all agree to take part," they added.