A drug with the potential to cause cancer in humans might have entered the food chain through horse meat slaughtered in UK abattoirs, Labour has claimed.

Shadow environment secretary and Wakefield MP, Mary Creagh told the Commons she had evidence that "several" horses slaughtered in the UK last year tested positive for the carcinogen phenylbutazone.

It's after a Dalepak factory in North Yorkshire was implicated in the horse meat in beefburgers scandal last week.

Agriculture minister David Heath told the Commons the Food Standards Agency checks all meat to ensure it is fit for human consumption

Where positive results of phenylbutazone are found the FSA investigates andtakes follow-up action to trace the meat.

Ms Creagh told the minister: "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.

She asked if Mr Heath was aware of the cases and the minister told her: "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.

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.

Ms Creagh has, however, confirmed this latest fears over horse meat is not connected to the horse meat in beef burgers scandal.