Rosie Bescoby of Pet sense based in North Somerset but covers Bristol. Used her last year and can 100% recommend her. Force free, realistic, sensible , hugely qualified and knowledgeable and a thoroughly lovely person to boot !
Yes, Rosie Bescoby would be high up my list too. Michelle Lord would also be suitable. Roz Pooley is also meant to be very good.
If it's a very serious case, there is a veterinary behaviour clinic at Langford (part of the University of Bristol vet school) that's meant to be good but it wouldn't be my first port of call as it's very expensive.