Tony Carroll is the latest trainer to have a horse test positive to morphine in England bringing the number to seven including a second horse from Sir Michael Stoute's stable.

It was confirmed earlier in the week the Stoute-trained Estimate, who is owned by The Queen, had tested positive after finishing second in the Gold Cup at Royal Ascot.

Stablemate Russian Realm has also shown traces of the drug following his unplaced Ascot run, although Stoute will wait for the results of the 'B' samples before making any further comment.

The first Carroll knew of the situation was when the British Horseracing Authority informed him Ocean Legend had tested positive for the drug after winning at Brighton on June 24.

It was the second of three victories the nine-year-old notched within a four-week period and he was tested after each success. The other two samples were clear.

The source of the drug is thought to be a batch of contaminated feed, with supplier Dodson & Horrell already undertaking a full investigation into the case.

"It was news to us and quite a surprise for it come up," Carroll said.

"It's just on of those things and I'm sure it will be sorted out. I don't know enough about it to comment on it.

"I'm sure it's just something that's gone through the food chain. Obviously a lot of trainers have had it and that's how it is."

Gay Kelleway also revealed she had a horse test positive for morphine, adding to fellow trainers Stoute, Eve Johnson Houghton and Charlie Hills to have been caught up in the current spate of positive tests for the drug.

The BHA confirmed on Thursday that a seventh horse had tested positive for the drug which is banned on race days.

A BHA statement said it could not rule out more positives as results from recent tests came in.