In reply to galpinos:
Best nearest - Weedon, it's ace but it's tiny
Most problems - Big Rock Bond in Bletchly
Old school, Pinnacle or Big Rock Hub
There is also a centre in Corby, but I've not been yet.
Further afield there is Climbing Station in Loughbourgh has loads to go at and great setting, Social Climbing (looks ace but I've not been) in Leicester, and if you like ninja warrior stuff Ape Index also in Leicester.
Basically Weedon if you only have a couple of hours, BR Hub if you have all day.
Post edited at 10:30