Brian Rowsell at Bristol & Wessex is very good. He's an ex Army Air Corps pilot, and still flies regularly with the Army as a TA pilot.
If you're prepared to travel further afield, Mike Smith at Heliair (Wellesbourne, near Stratford) is the most experienced heli instructor in the UK - and possibly the world. Without doubt the best civvy instructor I've ever had.
Good Luck.