In reply to franklin:
As far as indoors walls go within a reasonable driving distance (30 mins or so) of Aylesbury, Big Rock in Milton Keynes is pretty good, as is (so I am told, I have not climbed there myself) Oxford Brooke's. You also have walls in Amersham (The Climb) and Hemel Hempstead (The XC) that are both worth at least one visit as well.
Ive never had to rely on public transport so can't comment on how convenient the bus/train routes might be, but if it were me I would probably just hire a car at the airport and save the hassle.