Cameron is willing to participate in a single debate with all seven party leaders before the election campaign begins at the end of the month, his office said. Broadcasters had proposed three debates, including one between Cameron and Miliband.

The row comes as polls continue to show the Conservatives and Labor running neck-and-neck, with neither on course to gain a majority. That raises the prospect of weeks of negotiations leading to another coalition or a minority government reliant on smaller parties to get any legislation through Parliament.

Miliband reiterated he'd accept a challenge to a televised debate with just the prime minister. "He should stop ducking and weaving and name the date," he told BBC Television.

Liberal Democrat leader Nick Clegg, the deputy prime minister, accused the Conservatives of "lofty pomposity" and said he's ready to take the place of Cameron in a direct clash with Miliband.

"I am assuming the role of about the only person who's prepared to step up to the plate and actually defend the record of this government," Clegg said on his weekly phone-in show on LBC Radio Thursday. "If David Cameron's not prepared to do it, I am very happy to do it.

The BBC, Sky News, ITV and Channel 4 published new proposals in January for the debates to include smaller political parties after Cameron ruled out taking part unless those parties were given a chance.

The revised proposals include three debates, two of which would involve the leaders of the Conservatives, Labor, Liberal Democrats, the U.K. Independence Party, the Scottish National Party, the Green Party and Plaid Cymru.

Cameron denied putting hurdles in the way of the debates.

"If we hold the debates in the campaign, we won't talk about anything else, we'll only talk about the debates," he told Sky News. "That's one of the reasons three years ago, I said let's hold the debates before the campaign starts so that during the campaign we talk about some of the issues rather than simply the format of the debates."

Cameron previously declined to take part in the debates on the basis they excluded the Green Party and were therefore not representative. The original proposal only included the Tories, Labor and the anti-immigration U.K. Independence Party.