A vet should also be able to refer you to a reputable one - you will probably need to get the dog healthchecked anyway before a behaviourist will take a case on :)
Edited: was going to mail you privately but your email isnt displayed. Under APDT, Attila Szcukalek is listed as Norwich. Not sure what your problem is but he has an excellent reputation. He did a superb HTM routine at Crufts one year.
Sometimes a very good trainer can be better than a behaviourist because they may be more "hands on" with dogs and owners :) Just a thought.
Lindsay