The following links may be useful:

British Riding Clubs

BRC Area 1 (Riding Clubs in Scotland)

Official BRC Area 1 site

British Dressage

British Eventing

BSJA

Dressage Diagrams

Endurance GB

The Pony Club

The Scottish Horse

Scottish and Northern Equestrian

TREC UK

Dominique Parsons dressage (trainer at Rowallan)