Established providers:
Helicopter Services, Wycombe Air Park
PAS, Gloucester
Bond, Gloucester
'New' IR Providers:
Tiger Helicopters, Shobden
Fast Helicopters, Thruxton
Severn Aviation, Gloucester
The other 'established' schools will probably be just as busy as Bristows. You will probably be able to get a place sooner at one of the newer schools but I would personally be very wary of spending £20k+ without a decent track record.
I hope this helps.