A trainer for Sheikh Mohammed bin Rashid Al Maktoum's horses has admitted to a "catastrophic error" in using banned steroids to dope horses at the Dubai ruler's Godolphin racing stable.

Eleven horses tested positive for steroids, including stanozolol - the performance-enhancing drug used by disgraced Olympic sprinter Ben Johnson at the 1988 Seoul Olympics.

The trainer, Mahmood Al Zarooni, is to attend a British Horseracing Authority (BHA) disciplinary inquiry after the positive tests from horses in his care at Newmarket, southern England.

"I deeply regret what has happened. I have made a catastrophic error," Al Zarooni said on Godolphin's website.

"Because the horses involved were not racing at the time, I did not realise that what I was doing was in breach of the rules of racing. I can only apologise for the damage this will cause to Godolphin and to racing generally."

Godolphin racing manager Simon Crisford said the incident marked a "dark day" for Godolphin.

"Sheikh Mohammed was absolutely appalled when he was told and this is completely unacceptable to him. We will await the outcome of the BHA inquiry before taking any further internal action," he stated.

He has instructed me to begin an urgent review of all of our procedures and controls. That is already underway and we will take advice from the BHA in completing it," said Crisford.

Samples were taken from 45 horses at Godolphin's Moulton Paddocks Stables on April 9. Eleven samples were found to contain prohibited substances including ethylestranol and stanozolol.

One of the horses to test positive was Certify. The filly will not now be allowed to take part in the 1,000 Guineas at Newmarket next month.

Unbeaten in four career outings, Certify was one of seven horses to test positive for ethylestranol. Gold Cup runner-up Opinion Poll was one of four to test positive for stanozolol.

Founded in 1992, the Godolphin stable has won more than 2,000 races worldwide with winners in 14 countries.-Reuters