In reply to joss_bouncer:
Sea Walls, Avon Gorge (25M) - good tree anchors and or bolted anchors. Might be climbers but probably not.
Car Park Quarry, Goblin Combe (about 15M)- Good tree anchors and some good iron ground spikes. May be climbers but unlikely.
Most places at Symonds Yat (7M to 30M). More options than I can list. Great tree anchors all over the place and you will be able to find a place where there are no climbers easily.
There are places in Box Woods (Wilthsire) if you just want to get the principles of abseiling but they are loose and not recommended. There's a great looking old quarry there too but it's in someone's back garden
Andy