UK Independence Party leader Nigel Farage has accepted Nick Clegg's challenge of a public head-to-head debate over whether Britain should remain in the European Union.
Mr Farage said he had "no choice" but to pick up the gauntlet thrown down by the Deputy Prime Minister as there had been no "full national debate" on the issue for many years.
But he complained that David Cameron and Ed Miliband would not be involved, urging them to take part and accusing the Prime Minister of "running" from the challenge.
"I have battled on for 20 years," Mr Farage told LBC 97.3 radio - the same station on which Liberal Democrat leader Mr Clegg offered the debate 24 hours previously.
"I've been laughed at, ridiculed, attacked. But at no point in the 15 years I've been an MEP have we ever had a full national debate about the merits or demerits of EU membership .
"Therefore, when the Deputy Prime Minister says he wants to go public and have a debate with me on this issue, I have absolutely no choice.
"I have got to say yes because we need to have a national debate on what I think is the most important issue this country has faced for hundreds of years in terms of our constitution.
"So the answer is yes, but with one small caveat: I do really want for the Labour Party in the shape of Ed Miliband and the Conservative Party in the shape of the Prime Minister to join this debate as well."
"Downing Street said David Cameron was too busy running the country. Well running probably is the right word," he said of the Tory leader.
"But actually Mr Cameron, that is what the debate is about: who is running the country?"
Mr Farage said he had accepted the debate in part to increase the pressure for Ukip to be included in any televised party leaders debates during the 2015 general election campaign.
"If this works, and I see no reason why it shouldn't work, and if it engages a very large number of people in these European elections and in politics, then I think it makes it more likely that next year, for the general election, that everybody needs to be involved," he said.
"So I see this as being a step towards the same thing, on a bigger scale, happening next year.
"If Ukip can achieve in those European elections what I believe is potentially possible - and that is that we actually win a national election - how can they possibly keep us out of the leaders debates next year?"
Mr Cameron has made clear he does not believe Ukip should be represented if agreement is reached to repeat 2010's groundbreaking TV showdowns.
But Mr Clegg has raised concerns that his coalition partner could use Tory "anxieties" about the threat of Ukip as a reason not to agree to debates at all in 2015.
A Lib Dem spokesman said it was "great news" that the self-styled "party of in" Europe would be able to take on publicly the "party of out".
Negotiations will now begin over the details.
Mr Farage told one listener he was in no doubt that Mr Cameron and Mr Miliband would not take part.
"I'll have a fiver that they don't," he said.
A spokesman for Nick Clegg said: "It's great news that Nigel Farage has accepted the Deputy Prime Minster's challenge. It's going to be a lively debate and Nick is looking forward to it.
"Our two parties have a very clear position - Nick leads the party of in and Nigel Farage leads the party of out.
"Ukip want to yank us out of Europe and threaten our recovery, the Lib Dems wants to stay in Europe to protect British jobs.
"Both sides will now get together to discuss how we can make this happen."
A Green Party MEP demanded a voice for his party in the debate.
Keith Taylor said: "If there is to be a national television or radio election debate before the European elections then I fully expect the Green Party, which has representation in both Brussels and Westminster, to be invited."
"Only the Greens are offering people a chance to make a real change in these elections. We want to stay in the EU, but unlike the Lib Dems we support a referendum so we can all have a say.
"We want things in Brussels to change, but unlike Ukip we want to continue working with our European neighbours as part of the EU."