A score draw

A very quick blog on tonight's debate. This debate will define the campaign. A win for Clegg will cement the Lib Dem lead. A defeat, a gaffe or a clanger from Clegg will puncture the Lib Dem bubble for good. Watch for headlines like "flash in the pan"... basically putting Clegg back in his box for the rest of the campaign.

Another lacklustre, struggling performance for Brown will put the Labour party to bed for the election. Downbeat, almost invisible, in the last debate... Brown needs to elevate himself and get involved in the action. If he's nowhere, then the Labour vote will remain pitifully below 30%. Disastrous for Labour.

Cameron. All the pressure is on Cameron. He needs to find a way of dealing with Clegg without compromising all the work he's done since 2005 on dragging the Tories into the centre ground. Attack Clegg too much and it risks looking like a lurch to the right. Especially on foreign policy topics where basically the public has disagreed with Cameron on Iraq and Afghanistan... and where he can be exposed as breaking his "cast iron guarantee" on the Lisbon Treaty.

I doubt Clegg will do as well as last time. Cameron and Brown need to watch out for too blatantly copying Nick Clegg's technique... Brown is the favourite to stare awkwardly into the camera a la Clegg. But Clegg is likely to be able to pitch a good enough line on Iraq and Afghanistan to stay safe.

Cameron needs not to attack Clegg, but to give people a reason to vote Tory. The lack of difference between Labour and the Conservatives on foreign policy will make this difficult. Cameron needed this debate to be one where the are clear dividing lines between the parties. Unfortunately for him, the biggest dividing lines will be with the Lib Dems. Cameron risks appearing like Brown, whilst arguing that Brown would be a disaster.

My prediction? Cameron and Brown will be desperate. There is a chance of a big clanger from one of them. We've also seen Cameron recover from a dire situation before. He may tonight prove his bouncebackability once and for all and put in a serious performance. My hunch, though, given the subject matter will be a score draw. No clear winner tonight, setting it all up intriguingly for the last debate.

PREDICTION: Conservatives short of majority by 20