Please find below a selection of links that may be of use to you...

The British Horse Society
Represents and promotes horse riding in the U.K. and abroad, including training, welfare, safety, and career qualifications.

The British Showjumping Association (BSJA)
The BSJA is the governing body of show jumping in Great Britain, formulating the rules and codes of practice under which all affiliated competitions are held.

British Eventing
For information regarding eventing in the UK.

Trenerth Equestrian
Stud & AI Centre