Farage and Clegg
Nigel Farage and Nick Clegg will go head-to-headReuters

It's not exactly Muhammad Ali v George Foreman but Wednesday night's rumble in the Westminster jungle between Nick Clegg and Nigel Farage still holds out the prospect of some blood, if you can bear to sit through it.

The problem for the Tory party, however, is that some of the blood spilled might end up being David Cameron's. And he's not even taking part. Which is part of the problem.

Indeed, so allegedly disinterested is the prime minister in this knockout fight over Britain's place in the EU that he appears to have found a subsequent engagement to demand his attention.

When asked if Cameron would be listening, his spokesman told journalists: "I am not sure he will be able to. I don't think he will get the opportunity."

He might just as well have declared the prime minister was washing his hair that night.

So Cameron can find time for the Brits, apparently, but the first of the two-part bout between the most robust defender of EU membership (he says) and the man who wants to march the UK out somehow lacks the same draw.

You can't really blame him. He has, after all, spent years telling his party to stop "banging on about Europe" only to watch them sticking their fingers in their ears, after waving a couple of them at him, and continue banging.

David Cameron
David Cameron doesn't want to talk about EuropeReuters

He even may have been quietly relieved that Ed Miliband has finally ended the uncertainty about Labour's policy on a referendum by announcing official uncertainty. At least they were all agreed that the best plan is to just stop talking about it.

The trouble is, reality keeps crashing into the issue in the unlikely shape of Farage who is threatening to win the EU elections in May, a poll most people don't usually bother turning out for.

Thanks to Farage, this year could be very different as voters use the election to send their own two-fingered salute to the establishment parties, safe in the knowledge they aren't electing a government.

It is against that background that Clegg threw down the gauntlet to Farage, largely hoping that he could use the clash to boost his standing as the only man 100% committed to keeping Britain in the EU and exposing the real face of the Ukip leader.

And he could do well. But, then again, so could the charismatic Farage. Both sides have something to gain if they behave themselves. Clegg will have to drop his Mr Righteous mask, while Farage will have to ensure his own Mr Angry face doesn't break through his jolly exterior.

But, while they will spend plenty of time attacking each other, the figure of David Cameron clutching his referendum pledge will hover over the entire proceedings.

Clegg will claim the referendum would be a disaster which could threaten to destroy the country and that Cameron is held hostage by his Eurosceptics.

Farage will claim he doesn't believe Cameron will ever hold a referendum anyway and he will have gained some new status by being taken seriously enough to warrant such a debate.

Meanwhile, there will be the inevitable question of why Cameron hasn't deemed it important enough to even listen to, let alone take part in.

"I was washing my hair" won't do.