Broadcasters BBC, ITV, Sky and Channel 4 - have announced they intend to press ahead with previously-announced plans for three televised leaders' debates during the general election campaign, despite David Cameron saying he will only take part in one.
David Cameron's refusal to take part in the TV debates as planned is further damaging the reputation of politics, Green leader Natalie Bennett said.
Ms Bennett told the BBC the proposed format was "very fair" and "clearly reflected the desire of the British public to hear a wide range of political views".
"The fact is Mr Cameron, with his stance, is really doing further damage to trust in British politics," she said.
Prime Minister David Cameron will reveal himself to be a "weak leader" if he refuses to take part in the TV debates, Ed Miliband has said.
The Labour leader said: "It is make your mind up time for David Cameron.
"He can keep running from these debates with me and show himself to be a weak leader running from his record.
"Or he can agree to the debates which the British people deserve and that our democracy needs," he added.
David Cameron's director of communications has told broadcasters it is "disappointing" they will not take up the Prime Minister's offer of a single, seven-way TV debate.
Craig Oliver wrote to the broadcasters on Wednesday with Mr Cameron's "final offer" of a single 90-minute debate featuring at least seven leaders to take place before March 30.
But in a joint statement, the broadcasters said they would stick to previously announced plans for three debates in April.
Mr Oliver wrote back to the broadcasters saying: "I made the Prime Minister's final position clear in my last letter - he is willing to do a seven-way debate in the week beginning March 23.
"Clearly it is disappointing that you are not prepared to take him up on that offer.
"I am ready to discuss at your convenience the logistics of making the debate we have suggested happen."
A British Airways' plane with more than 200 passengers on board has landed safely after having to return to London following a suspected technical problem.
The Boeing 777 - flight BA49 - had left Heathrow Airport at around 2.35pm today bound for Seattle in the USA.
It reached a point north-west of Edinburgh when the cockpit crew made the decision to return to Heathrow.
Scottish National Party leader Nicola Sturgeon has said she is pleased that the Prime Minister's "bluff has been called" on the issue of the three televised leaders' debates.
Labour leader Ed Miliband has said it is now "make your mind up time" for David Cameron over the TV debates, ITV News Deputy Political Editor Chris Ship tweeted.
It comes after broadcasters confirmed they will go ahead with their plans for three televised leaders debates.
A British Airways' plane has had to turn back to London after a suspected technical problem.
The Boeing 777 - flight BA49 - had left Heathrow airport around 2.35pm today bound for Seattle in the USA.
It reached a point north west of Edinburgh when the cockpit crew made the decision to return to Heathrow where the plane was expected to land around 4.40pm.
BA said the plane was carrying 218 passengers and 14 crew.
Ukip leader Nigel Farage said he would "accept the challenge" of taking part in the TV leaders' debates.
Mr Farage said he was pleased the broadcasters had stood firm over their plans but said he preferred their earlier proposal for a four-way debate featuring himself, Mr Cameron, Mr Miliband and Mr Clegg rather than the proposed seven-way.
He said: "I'm pleased that the broadcasters have stood firm at last but it would have been far better had they stuck with their original proposal which included fewer parties. But nonetheless we accept the challenge."
Deputy Prime Minister Nick Clegg has called on David Cameron to join the debates in a message on Twitter, saying "you haven't got your own way so accept it and take part".