Farage Clegg
Nigel Farage and Nick Clegg will face each other in a live TV debateReuters

Ukip leader Nigel Farage and Liberal Democrat deputy prime minister Nick Clegg will face each other in a live TV debate before the European elections in May.

In an hour-long broadcast on 2 April refereed by David Dimbleby, Farage will argue his case for withdrawal from the EU while Clegg has promised a robust defence of British membership of the union.

Inevitably, within moments of the details being made public, the question was raised in Westminster of whether the other party leaders would join in.

It is the wrong question. The real question is: why on earth would they want to, what could possibly be in it for them?

David Cameron and Ed Miliband are now in the position where they can sit back and watch as the two smaller parties, their political rivals, kick big chunks out of each other to the nation's undoubted enjoyment if not necessarily enlightenment.

And the phrase you will not be hearing much, particularly from the prime minister, is: "I agree with Nick". That died shortly after those heady general election debates in 2010 when it briefly appeared Clegg was flavour of the month and everyone wanted to look like his best pal.

Will Cameron be tempted at any point to declare: "I agree with Nigel" though? After all, he needs to win over those Ukip sympathisers both inside and outside his own party. It would be a risky move.

So far neither Cameron or Miliband have shown any enthusiasm for joining this particular mud-wrestling match.

But it would be risky to entirely rule out the possibility that the option of some free TV exposure might just appeal to their egos.

The biggest effect of that, however, would be to give power to Farage's claim that he should be included in any pre-general election TV debates. And they don't want that, do they?

This whole affair erupted when Clegg threw down the challenge to Farage last month. The Ukip leader said he wanted it to include all four leaders, but eventually decided to make do with Clegg.

Ukip has shown recently that it is pushing the Lib Dems into fourth place in the polls and by-elections so there could be quite a lot riding on the debates. A battle for third place at the very least.