LONDON Britain's Food Standards Agency (FSA) said six horses slaughtered in the UK that tested positive for the drug phenylbutazone were exported to France and may have entered the human food chain.
Phenylbutazone, commonly known as bute, is an anti-inflammatory painkiller for sporting horses but banned for animals intended for eventual human consumption as it is potentially harmful.
Britain's food regulator said on Thursday it was gathering information on the six carcasses sent to France and will work with the French authorities to trace them.
The FSA said it checked 206 horse carcasses between January 30 and February 7. Of these, eight tested positive for the drug.
It said the six sent to France were slaughtered by LJ Potter Partners at Stillman's (Somerset) Ltd in Taunton, western England.
The remaining two did not leave the slaughterhouse in the UK - High Peak Meat Exports Ltd, Nantwich, north west England - and have now been disposed of.
The FSA introduced 100 percent testing of horse carcasses on January 30 in response to the growing horse scandal.
The issue first came to light on January 15 when routine tests by Irish authorities discovered horsemeat in beef burgers made by firms in Ireland and Britain and sold in supermarket chains including Tesco, Britain's biggest retailer.
Concern grew last week when the British unit of frozen foods group Findus began recalling its beef lasagne on advice from its French supplier, Comigel, after tests showed concentrations of horsemeat ranging from 60 to 100 percent.
The revelations, affecting a growing number of countries, processors and retailers, have raised uncomfortable questions about the safety of the European food supply chain and prompted governments to send out a European Union-wide alert.
Earlier on Thursday a British parliamentary report into the scandal said discoveries so far of horsemeat in products sold as beef are likely to be the "tip of the iceberg".
(Reporting by James Davey; editing by Neil Maidment)