In reply to andymac:
It's said that pain in front of the knee generally indicates a saddle too low and behind the knee, too high.
Have you tried sitting on the bike with the crank at the bottom and your leg hanging loosely? Your heel should just contact the pedal. Don't straighten your leg.
If the pain continues go and see a physio who specialises in bike setup. If you're in Lancashire I recommend Nick Dinsdale in Clitheroe, he's very fussy.