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The Prime Minister has expressed concern that the leaders' TV debates could detract from "issues" in next year's general election, despite saying he thought they were "good".
Speaking on The Agenda, he said the debate on ITV before the last election "took all the life out of the rest of the campaign" and became a "commentary on who was doing well or badly in the TV debates".
He also said he didn't think Ukip could be included in the debates without offering the same opportunity to the Green Party.
Watch the full discussion on The Agenda on ITV at 10.35pm tonight
Broadcasters announced their plans today for a series of televised debates between party leaders in the run-up to the next year's general election.
Providing he agrees, Ukip leader Nigel Farage will join David Cameron, Ed Miliband and Nick Clegg in one of the debates.
But a lukewarm reception from the Prime Minister and a possible legal challenge from the Green Party suggest this is not a done deal.
ITV News' Political Correspondent Libby Wiener reports:
The leader of the Respect party, George Galloway MP, has said he is ready to join the Green Party in a legal challenge over next year's leader TV debates.
Both parties have been denied the opportunity to send a leader to the debates.
Labour Leader Ed Miliband has welcomed the televised debates and warned Prime Minister David Cameron not to put up "false obstacles" to them going ahead.
Mr Miliband said the most important thing was to give the public "what they're entitled to" with the TV debates.
"They happened in the last General Election. We must make sure they happen in this General Election," he added.
The Green Party is seeking legal advice over its exclusion from planned TV debates ahead of the General Election, according to Caroline Lucas, MP for Brighton Pavilion and former leader of the party.
Prime Minister David Cameron says he in favour of plans for televised debates with each of the main party leaders ahead of next year's General Election.
But he questioned why the proposed debates could not be spread out over a longer period and why some political parties had been included and others excluded.
Prime Minister David Cameron has said he is in favour of plans for televised debates ahead of the General Election.
But the Conservative Party leader said the proposal had to be one "everyone agrees to".
Broadcasters are "out of touch" by excluding the Green Party from the proposed televised debates ahead of the General Election, leader Natalie Bennett said.
She said: "With these proposals the broadcasters are demonstrating just how out of touch they are with the public mood, and how ridiculously they cling to the idea that the future of politics looks like the past."
The Green Party leader said it was clear from votes and polls that the public were "fed up with the three business-as-usual parties" and were looking around for alternatives.
The party's supporters would be "seriously short-changed by debates from which we were excluded," Ms Bennett added.
Responding to the proposals put forward by broadcasters for three televised debates ahead of the General Election, a spokesman for the Conservative Party said: "We note the request and will respond accordingly."
Televised debates involving the party leaders should be a permanent feature in General Election campaigns, ITV's Director of News and Current Affairs Michael Jermey said.
Latest ITV News reports
The invite to participate in TV debates ahead of the election has been delivered - it's now up to the political leaders to accept or refuse
ITV, BBC, Channel 4 and Sky have revealed their plans for a series of live party leader debates in the run up to the 2015 General Election.