Trainer Hughie Morrison has expressed his relief at being found not to blame after one of his horses failed a drugs test at the start of the year.

Morrison could have been banned from the sport for up to 10 years as a consequence of Our Little Sister's positive test for the anabolic steroid nandrolone following a race at Wolverhampton on January 14.

But an independent disciplinary panel of the British Horseracing Authority has announced the banned substance was administered intentionally "by person or persons unknown, for unknown reasons", giving Morrison the minimum fine of STG1000 ($A1700).

"There's no ban. We've been completely exonerated, so the hell of the last 11 months can be forgotten," Morrison told Press Association Sport.

"All my staff are having a celebration now and it's very emotional."

The 57-year-old trainer accepted he was technically in breach of the BHA's strict liability anti-doping rules as a result of the positive test, but vehemently denied any wrongdoing and offered a cash reward for anyone that could help prove his innocence.

"I cannot overstate the stress that has been caused by this long running case both for me, my wife, all my staff and connections and the relief now felt having been rightly and so comprehensively exonerated," Morrison said in a statement.

"The culprit who injected the filly is still out there so everyone needs to be on their guard."

An independent disciplinary panel agreed with Morrison's legal team that the trainer had not administered the prohibited substance, nor had any of his staff or service providers - or anyone else under his control.

The panel also suggested that Our Little Sister may have been given the banned substance "to target Mr Morrison, but even that remains speculative".