David Cameron has agreed to take part in just one televised leaders' debate ahead of the general election in a "final offer" to broadcasters.
The Prime Minister has ruled out turning up for a head-to-head with Ed Miliband and will only sign up for one 90-minute contest involving at least seven party leaders to be held before March 30.
Downing Street told broadcasters to scale back their plans for a series of three debates involving Mr Cameron and blamed organisers for their "chaotic" negotiations.
M r Cameron's latest terms for taking part have been set out in a letter to Sue Inglish, the chair of the broadcasters' leaders' debates committee, by his director of communications Craig Oliver.
It states: " In order to cut through this chaotic situation I am willing to make the following proposal: There should be one 90-minute debate between seven party leaders before the short campaign.
"As well as the Prime Minister, the leaders of the Green Party, Labour, Liberal Democrats, Plaid Cymru, SNP and Ukip should invited.
"The leader of the DUP should be allowed to make his case for why he should be involved. If the broadcasters cannot agree amongst themselves who hosts the debate, lots should be drawn, though the debate should be freely available to whoever wants to broadcast it.
"In order for it to be organised in time, the debate should take place during the week beginning March 23. I will make myself available to negotiate the details. Having been the editor of numerous broadcast news and current affairs programmes, I know this is ample time to organise a programme.
"This is our final offer, and to be clear, given the fact this has been a deeply unsatisfactory process and we are within a month of the short campaign, the Prime Minister will not be participating in more than one debate."
Deadlock over the debates prompted Sky News and Channel 4 earlier to offer to host a head-to-head clash between the Prime Minister and the Labour leader on a date of the politicians' choosing and Mr Miliband went on to say he was prepared to take part "any time, any place, anywhere" in an attempt to force the premier's hand.
But No 10 sources said the "only real option" left was one debate because time was running out ahead of the May 7 poll, and insisted the "fairest way forward" was with at least seven party leaders.
They branded the whole process a "shambles" and said broadcasters needed to "have a long hard look at themselves" over the way it had been handled.
Mr Cameron has been "crystal clear" on his position on the debates for two years since saying he wanted them to be held earlier because he believed they "sucked the life" out of the campaign last time round, the source added.
Labour sources accused the Tories of doing everything they can behind the scenes to "scupper the negotiations and sink the debates".
In a joint statement, broadcasters said: " The BBC, ITV, Channel 4 and Sky have received an email from the Prime Minister's office with a proposal. The broadcasters are committed to providing our audiences with election debates.
"Twenty two million people watched the debates in 2010 and we believe the debates helped people to engage with the election.
"The broadcasters have set out their proposals and continue to talk to all the relevant parties on an equitable basis.
"We will respond to the Conservatives' proposal in due course."
Douglas Alexander, who is leading Labour's general election strategy, said: "We continue to support the broadcasters' proposals, including for seven-way debates alongside a two-way debate.
"But this is an outrageous attempt from the Prime Minister to bully the broadcasters into dropping their proposals for a head-to-head debate between David Cameron and Ed Miliband.
"That it comes only hours after Ed Miliband called David Cameron's bluff and said he would debate him any time, any place, shows the lengths David Cameron will go to run scared of a debate with Ed Miliband."