Badminton Horse Trials has added its voice in the fight against allowing bute in equestrian competition.

Hugh Thomas, director of the international event has written to FEI president Princess Haya urging her to “do whatever is necessary to change or suspend this decision, and to do so urgently”.

In his open letter to the president, Mr Thomas said the Badminton Horse trials team is “utterly committed” to running the event “in the spirit of clean sport”.

He said he is “very unhappy” at the prospect of being asked to run an event under the new rules.

“We believe that if a horse needs these drugs to appear sound, whether in actual competition or at the horse inspections, he should not take part in the competition,” he said.

“The soundness or otherwise of a horse is integral to the three-day event, which is a test not only of his ability and his rider’s, but also to his fitness and soundness.”

Mr Thomas’s letter follows a barrage of correspondence to the International Equestrian Federation (FEI) from leading vets around the world.

Leading endurance vet Dr Fred Barralet, together with 19 of his colleagues, wrote to Princess Haya earlier last week.

He warned the use of non-steroidal anti inflammatories could cause “catastrophic breakdown” in the endurance horse, in which the use of bute is particularly damaging.

Dr Barrelet, from equine veterinary specialist practice Rossdales & Partners in Newmarket, said the change in FEI policy is “the cause of utmost concern for FEI endurance event and treatment vets”.