Mike Bill down at
London Helicopters at Redhill has a good reputation, and Mike Smith for
Heli Air up at Wellesbourne would be worth a look too. Bravo73 has hit it on the head, decide where and with whom you would like to work and go for there. You could also ask Fred Cross at the CAA since he has contact with most of the schools and instructors. Whilst I'm sure he wouldn't be so indiscreet as to express a preference, he will be able to tell you the lie of the land.