The first ever prime-ministerial debate will be remembered not - as so many predicted - for a gaffe or a scripted put-down or a bead of a sweat. It will be remembered as a serious debate about serious issues and, I suspect, the first of many election debates to come.

Politically it is the emergence of Nick Clegg as a serious player in this election which will prove to be most significant. The Liberal Democrat leader was given a great opportunity to introduce himself to the millions of voters who scarcely knew him and he took it with gusto.

The question is whether instant polls suggesting that he "won" the debate can be converted into increased support for his party. If so, what matters is where will that support come from.

With a hung parliament a very real possibility, and with many voters saying that they like the idea of parties working together, the Lib Dems are certain to find themselves wooed, attacked and scrutinised with renewed vigour.

The dynamic between David Cameron and Gordon Brown, their personalities and their policies did not fundamentally change as a result of this debate, but there is now a third unpredictable factor at play with three weeks to go and two more debates.