A potentially carcinogenic drug may have entered the food chain through horse meat slaughtered in the UK, Labour has claimed.
Shadow environment secretary Mary Creagh told the Commons she had evidence that "several" horses slaughtered in the UK last year tested positive for the carcinogen phenylbutazone.
Her claim comes days after the separate revelation that burgers sold by some supermarkets contained traces of horse meat. Ms Creagh said: "I am in receipt of evidence showing that several horses slaughtered in UK abattoirs last year tested positive for phenylbutazone, or bute, a drug which causes cancer in humans and is banned from the human food chain. It is possible that those animals entered the human food chain."
Agriculture minister David Heath replied that the Food Standards Agency (FSA) checked all meat to ensure it was fit for human consumption, saying: "The Food Standards Agency carry out checks in slaughterhouses to ensure that equine animals presented for slaughter are fit for human consumption in the same way as they do for cattle, sheep and other animals.
"In addition, the FSA carry out subsequent testing for phenylbutazone and other veterinary medicines in meat from horses slaughtered in this country. Where positive results for phenylbutazone are found, the FSA investigates and takes follow-up action to trace the meat."
Ms Creagh questioned whether that meant Mr Heath was aware of the issue. "I'm astonished that you have not raised this and I think the public have a right to know," she said.
The claim that bute could have entered the food chain follows the revelation that burgers sold by Tesco and other supermarkets contained traces of horse meat. Ten million burgers have been taken off supermarket shelves across Ireland and the UK as a result of the scandal. Suppliers in the Netherlands and Spain have been identified as the possible sources for incorrectly labelled ingredients.
Responding to Ms Creagh's claims, the FSA said: "Horses which have been treated with phenylbutazone or 'bute' are not allowed to enter the food chain.
"The FSA carries out checks in slaughterhouses to ensure that horses presented for slaughter are fit for human consumption, in the same was as they do for sheep and cattle, etc. The FSA also carries out regular enhanced sampling and testing for phenylbutazone in meat from horses slaughtered in the UK."
The FSA added: "During the recent horse meat incident the Food Safety Authority of Ireland (FSAI) checked for the presence of phenylbutazone and the samples came back negative."