The British Food Standards Agency (FSA) released a report on Thursday confirming the presence of the drug phenylbutazone (bute) in horses slaughtered in Britain which may have entered the food chain. However, the level of bute in horse meat presents a "very low risk" to human health, experts said.

According to the report, the FSA's most recent tests on the presence of bute checked 206 horse carcasses slaughtered between Jan. 30 and Feb. 7. Of these, eight tested positive for the drug. Six of the eight were sent to France and may have entered the food chain. The remaining two have now been disposed of in accordance with EU rules.

The FSA said it was gathering information on the six carcasses sent to France, and would work with French authorities to trace them.

Since end-Jan, the FSA has been testing all horse carcasses for bute, and from this week, a "positive release" system for horses slaughtered in Britain has been in operation, which means that all horse carcasses have to test negative for bute before they can enter the food chain.

Bute is not allowed to enter the food chain. However, according to Dame Sally Davies, the chief medical officer of the Department of Health, horsemeat containing bute presents a "very low risk" to human health.

"Phenylbutazone is a commonly used as medicine in horses. It is also prescribed to some patients who are suffering from a severe form of arthritis. At the levels of bute that have been found, a person would have to eat 500 to 600 burgers a day that are 100 percent horse meat to get close to consuming a human's daily dose," Davies said.

"In patients who have been taking phenylbutazone as a medicine there can be serious side effects but these are rare. It is extremely unlikely that anyone who has eaten horse meat containing bute will experience one of these side effects," he added.