A metabolite of cocaine was the substance found in a test taken from the unbeaten $1.4m horse Walk In The Sun after he won at Lingfield in February. Jeremy Noseda, who trained the horse at the time, declined to comment about the positive test when contacted on Monday night.

“I have no comment on anything at all,” was Noseda’s response. Both he and the British Horseracing Authority have remained tight-lipped since word got out at the end of March that the horse had failed a dope test. Noseda’s home town of Newmarket has, however, been rife with gossip about a subject that the Guardian has now been able to establish as fact.

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It is normal for racing’s ruling body to delay for some months before issuing charges after a positive test. This is particularly true where the source of the prohibited substance is in dispute, which is certain to be the case with Walk In The Sun.

It took almost all of last year for the BHA to wrap up a case involving the trainer Hughie Morrison, who was fined £1,000 in December after a horse of his returned a positive test for a steroid in January. Morrison maintained his innocence throughout, and was believed by the disciplinary panel, in a case that exposed the limitations of the BHA’s “strict‑liability” regime on anti-doping.

Noseda is expected to face charges in due course, because of the BHA’s long established principle that a trainer is strictly responsible for his horses and for anything found in their systems. He would avoid charges only if the BHA were satisfied, after investigation, that it had discovered an explanation for the positive test that exonerated him.

This is not the first time Noseda has faced questions over an unexplained substance turning up in the sample of one of his horses. In 2016 he was fined £2,000 for two separate positive tests returned the previous year by Librisa Breeze. One of those occasions related to a finding of temazepam in the grey’s system after he ran at Windsor in June 2015 and that sample was also found to contain a metabolite of cocaine after further examination. The BHA’s panel eventually accepted that the source was unexplained.

It has been a turbulent few months for Noseda, who had much reason for optimism at the start of the year, thanks to the investment in his yard by the big-spending Phoenix Thoroughbreds, owners of Walk In The Sun. But Phoenix withdraw their 14 horses from his Shalfleet Stables a month ago, to the trainer’s evident ire.

He responded by tweeting: “I am shocked and surprised by their decision. I have no reason or explanation.” It was the most recent activity on his Twitter account and his stable has been left notably quiet in recent weeks. He had just three runners in May, none of them within the past fortnight, and has a single entry for the next seven days.

His dismay at the loss of the Phoenix horses will have been compounded on Saturday night when one of them, Gronkowski, ran second in the enormously valuable Belmont Stakes. The horse ran in the name of the US trainer Chad Brown, who inherited him mere weeks ago and was quick to praise the condition in which the horse arrived at his yard.

Walk In The Sun, meanwhile, has joined the Wiltshire-based trainer Martyn Meade and is expected to run at Royal Ascot next week, in the St James’s Palace Stakes. The BHA has no objection to the three‑year‑old colt resuming his racing career, on the basis that the substance found in his sample in February would long since have cleared his system and would have no residual performance‑enhancing effect.

There was no further comment from the Phoenix ownership operation, whose Tom Ludt declined to discuss the positive sample when approached last week. Of the decision to end its alliance with Noseda, Ludt said: “We moved the horses for business reasons, which was in the best interest of Phoenix but not just one issue.”

A BHA spokesperson said: “It is BHA policy not to comment on investigations or speculation surrounding potential investigations.”

Meanwhile, the former champion jockey Jim Crowley ended his silence about an altercation with a fellow rider at Goodwood on Sunday which left him with a split lip. Raul Da Silva was held responsible by the stewards, who suspended him for 21 days. Crowley said yesterday that he had been struck by “what felt like a piece of lead”, as a result of which the BHA may reopen its investigation into the incident.