I saw HH's post re the BMC and i have alluded to similarities between the BMC and GAGB in the past.

One organisation represents climbers in the UK.

They discuss access, environment and liase directly with landowners.

They are quite big and have paid up members.

The BMC organise regular crag clean up days a CITO approach would probably be good way to get in touch.

Bear in mind cleaning sometimes mean route cleaning on a big dangly rope h34r:

http://www.thebmc.co.uk/Pages.aspx?page=152