Top trainer Willie Mullins has been fined and one of his horses disqualified from a race at the Cheltenham Festival after it was found to have run with a “prohibited substance” in its system.

An investigation into a failed doping test also revealed CCTV footage of the stables had been “misplaced”.

Final Demand finished second in the Brown Advisory Novices’ Chase at Cheltenham in March.

An independent British Horseracing Authority disciplinary panel said: “Final Demand ran in the Grade One event at the Festival on March 11 with a Category B Prohibited Substance (mepivacaine) in its body”.

Mepvicane is a local anaesthetic commonly used to treat racehorses.

The panel added that Mullins “failed to declare use of mepivacaine on the horse in its medical declaration forms submitted prior to the race”.

Expert evidence suggested the “low dose… entered the horse very close to the time of sampling” and the investigation was unable to ascertain how it happened, given the precautions taken at the yard.

“There is no suggestion that Mr Mullins or any of his staff knew of any administration of mepivacaine, and the BHA accepts that reasonable precautions were in place,” judicial panel chair Sarah Crowther KC. Mullins was fined £1,100.

In the course of the investigation it emerged CCTV footage of a yard where the horse was kept had not been retained, which racecourses are required to do.

The panel was informed “that the hard drive containing the footage had been misplaced”.

However, Crowther said this fact should not be “overstated” as the horse had been moved to a different yard at the time of receiving the dose and that that footage was obtained and reviewed.

Cheltenham was fined £5,000 for that rule breach.