A potentially harmful horse drug has entered the human food chain in France, a UK minister said on Thursday. Elsewhere doubts have been raised over French company Spanghero's denials they knowingly bought horsemeat.

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An equine drug that is potentially harmful to humans has entered the human food chain in France via three horse carcasses exported from Britain, British agriculture minister David Heath said on Thursday.

But Heath said the drug phenylbutazone, which can cause a serious blood disorder in humans in rare cases, had not been found in tests on products made by food giant Findus, which is embroiled in a Europe-wide horsemeat scandal.

Elsewhere on Thursday French company Spanghero was billed for 42 tonnes of horsemeat, a French newspaper reported. The news casts doubt on the company's claim to have never knowingly bought or sold the meat at the centre of a Europe-wide scandal.

French daily Le Parisien published a bill dated January 4 that was made out to Spanghero and printed on the headed paper of Draap Trading, the Dutch-run, Cyprus-based intermediary which sourced meat in Romania for Spanghero.

The bill contains the numbers 0205 0080, which the paper said was an international code for frozen horsemeat. Spanghero did not immediately respond to AFP's request for an explanation of the bill.

Le Parisien said Romanian authorities had shown it three similar bills. In total, the bills add up to orders for 42 tonnes of minced offcuts – the fat, tendons and other pieces left over after the horse has been deboned and the prime cuts removed.

Romanian officials have been angered by what they see as an attempt by the French companies involved in the scandal to point the finger of blame at their abattoirs.

They insist horsemeat leaving their slaughterhouses would have been clearly labelled as such and that the fraud must have occurred further along the food chain.

Spanghero said in a statement earlier this week that it did not "sell, re-sell or process horsemeat in any form." In a statement to Le Parisien, the company denied receiving any bill for horsemeat from Draap Trading.

The horsemeat Spanghero received was passed on to another French company, Comigel, which was responsible for using it in frozen ready meals which were labelled as 100 percent beef.

Comigel insists it could not have known the meat it was using was horsemeat and that it alerted authorities immediately once it knew there was a problem.