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."

Agriculture minister David Heath said that the Food Standards Agency (FSA) checked all meat to ensure it was fit for human consumption, saying: "The Food Standards Agency carries 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 carries out testing for phenylbutazone and other veterinary medicines in meat from horses slaughtered in this country. Where positive results for phenylbutazone are found, the FSA takes follow-up action to trace the meat."