Here are some links which you may find useful.

British Horseracing Authority
British Equestrian Federation
British Horse Society
British Eventing
British Showjumping
British Dressage
Nation Trainers Federation
British Equestrian Trade Association
The Pony Club
The Association of British Riding Schools

South Essex Insurance Brokers
Shearwater Insurance
NFU Mutual Insurance
Petplan Equine
Equine & Livestock

Legal and Mediation
Ashfords Solicitors
Barlow Lyde & Gilbert Solicitors
Berrymans Lace Mawer Solicitors
Blythe Liggins Solicitors
Bond Pearce Solicitors
Brechin Tindal Oatts
Browne Jacobson
Charles Russell Solicitors
CIP Solicitors
Clarke Willmott
Crill Canavan
Davies Arnold Cooper Solicitors
Edmondson Hall Solicitors
Foot Anstey Solicitors
Forbes & Partners Solicitors
Greene & Greene Solicitors
HBM Sayers Solicitors
Hegarty Associates
Herbert Mallam Gowers Solicitors
Hextall Erskine Solicitors
Hill Dickinson
Hugh James Solicitors
Irwin Mitchell Solicitors
Keoghs LLP
Knights Solicitors
Leigh, Day & Co
Leo Abse & Cohen
Lyons Davidson Solicitors
McCollum & Co Solicitors
Morgan Cole
Osler Donegan Taylor Solicitors
Pannone LLP
Paull & Williamsons Solicitors
Penningtons Solicitors
Plexus Law
Reynolds Porter Chamberlain LLP
Russel Jones & Walker
Shaffrey & Co
Shaw & Co Solicitors
Simpson & Marwick Solicitors
Stewarts Law LLP
Swayne Johnson Solicitors
Taylor Joynson Garrett
Taylor Vinters
Trethowans Solicitors
Weightmans LLP
Withy King
Wolferstans Solicitors
Wright Hassall LLP
Zimmers Solicitors Rechtsanwlte Abogados

Mediators, USA