Pathologist Sir Colin Berry says the notion that there may be "a clinically significant amount" of the potentially carcinogenic drug phenylbutazone in horsemeat "is frankly, daft."
The Food Standards Agency has dismissed claims that the horse drug 'bute' may have entered the human food chain in horsemeat.
The FSA said horses treated with the drug phenylbutazone are "not allowed to enter the food chain".
The FSA statement added: "During the recent horsemeat incident the Food Safety Authority of Ireland checked for the presence of phenylbutazone and the samples came back negative."
Shadow Environment Secretary Mary Creagh earlier expressed fears that the drug may have entered the food chain through horsemeat slaughtered in UK abattoirs
A toxicologist from Leeds University has played down claims from Labour's shadow environment secretary Mary Creagh that the drug phenylbutazone causes cancer in humans.
Professor Alistair Hay said there is "no convincing evidence of carcinogenicity".
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.
– FOOD STANDARDS AGENCY
In 2012 the FSA identified five cases where horses returned non-compliant results. None of the meat had been placed for sale on the UK market. Where the meat had been exported to other countries, the relevant food safety authorities were informed.
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.
Shadow Environment Secretary Mary 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."
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 Mary Creagh told the Commons she had evidence that "several" horses slaughtered in the UK last year tested positive for the carcinogen phenylbutazone.
Agriculture minister David Heath told the Commons the Food Standards Agency checks all meat to ensure it is fit for human consumption.
He told MPs:
Where positive results of phenylbutazone are found the FSA investigates and takes follow-up action to trace the meat.