Nick Clegg's decision to challenge  Nigel Farage to a head-to-head debate on the EU is the latest stage of his attempt to frame the Lib Dems as "the party of in" against UKIP, "the party of out". Europhilia might not be a popular stance in British politics but Clegg's calculation is that an unambiguously pro-European pitch will appeal to his party's target audience. He said on his LBC show this morning: "I’ll tell you what I’ll do. I will challenge Nigel Farage to a public, open debate about whether we should be in or out of the European Union. That’s the choice facing the British people.
"He is the leader of the party of OUT, I am the leader of the party of IN. It’s time for a proper public debate so that the public can listen to the arguments and decide for themselves."
Farage has responded  by demanding that Cameron and Miliband are also included "in order that the British people can see all their main political leaders argue their positions". With that condition unlikely to be met (Cameron will never debate Farage), it is unclear whether he will take Clegg alone. We are told that Farage "will give a full response to this development on LBC tomorrow morning".
But what of the main leaders' debates? The Lib Dems and Labour are ready to sign up for  the "333" model: three debates between three leaders over three weeks. But the Tories, who blame the debates in party for their failure to win a majority in 2010, are stalling. Cameron has long complained that the debates "sucked the life" out of the campaign and is wary of committing to a repeat.
But one option under discussion in Conservative circles, as I first reported  last September, is a one-on-one debate between Cameron and Ed Miliband, ideally before the campaign begins. Aware that Cameron outpolls both his party and Miliband, the Tories have long intended to frame the election as a presidential contest ("do you want David Cameron or Ed Miliband as your prime minister?") and a debate would be the ideal way to amplify this impression. A one-on-one debate between Cameron and Miliband would also eliminate the need to specifically exclude Nigel Farage. Conservative whip Greg Hands gave the game away when he tweeted  during the German leaders' debate: "Interesting that German TV debate only has the leaders of the two parties who could conceivably be the Chancellor. No FDP, Greens, etc".
A Farage-Clegg debate could provide the Tories with the opening they need to argue explicitly for a Cameron-Miliband debate. As the europhile and the europhobe play in the corner, they can declare that it's time for the two men fighting to become prime minister to take each other on.