Wot No Exit Poll?

I don't know if anyone else has commented on this but it's been bugging me since 10pm last night and I can't find anything on any of the other likely political blogs (please correct if I'm missing it somewhere): What happened to the customary BBC exit poll? Normally, whenever polls close, the BBC is the first to predict the eventual result based on its exit poll. Did they really not conduct one (if so, why not)? Or was the result so bad for Labour that they decided not to reveal the results and hope that over a 24 hours period of results trickling in, we would all get bored and not notice that the night had been a veritable disaster for Labour and an incredible success for the Conservatives?

Not that the BBC is biased in any way, of course...