Eight horses slaughtered for food in the UK have tested positive for the veterinary painkiller phenylbutazone, known as bute, new tests from the Food Standards Agency (FSA) revealed on Thursday.
The minister for food and agriculture, David Heath, told the Commons that 206 carcasses had been tested. Six of the carcasses that tested positive may have entered the food chain in France in the last few weeks, according to the FSA, and efforts are being made to recall them.
Heath said the Findus lasagne found to contain horse had tested negative for bute. The FSA confirmed that all tests on the food products analysed so far, including Tesco burgers, were negative.
The shadow environment secretary, Mary Creagh, told Heath she had raised the issue of bute three weeks ago: "Can he explain why, up until four days ago, all horses were being tested for bute but were still being released for human consumption? In the middle of a horsemeat adulteration scandal, that is catastrophic complacency."
Dame Sally Davies, the UK's chief medical officer, said: "The trace levels detected are very unlikely to have harmed any human, child or foetus."
She said a person would have to eat more than 500 horsemeat burgers to get a harmful dose and that the doses people may have received if bute had got into food were "less than 1% of any dose that had ever given an adverse effect".
The Guardian has discovered that the results from two carcasses that tested positive for bute in 2012 – out of a total of nine – were not reported to the FSA for up to seven months. In July 2012 the veterinary residues committee (VRC), which advises the government, warned that it had repeatedly expressed concern about bute entering the food chain.
The VRC said bute had "the potential for serious adverse effects in consumers, such as blood dyscrasia [a rare but life-threatening condition]".