Ministers are struggling to reassure consumers over the horsemeat scandal after tests revealed potentially dangerous contamination of meat with veterinary drugs and Asda confirmed the first trace of horse had been found in a fresh beef product.
Overwhelmed laboratories are warning that the industry may not fully comply with Friday's deadline for completing tests for horse in all beef products, raising the prospect that the government will be unable to give British food a clean bill of health for days.
Medical risks from eating horse containing the equine painkiller phenylbutazone, or bute, are said to be very low but David Heath, the food minister, revealed on Thursday that eight horses slaughtered for food in the UK had tested positive. Six of those carcasses had been exported to France for use in human food in the last few weeks, according to the Food Standards Agency, but efforts were being made to recall them.
The Guardian has also learned that two positive tests for bute in 2012 were not reported to the Food Standards Authority (FSA) for seven months.
On Thursday police arrested three men on suspicion of offences under the Fraud Act as part of their investigation into the mis-selling of horsemeat as beef. Dyfed Powys police said they were being held at Aberystwyth police station following arrests at abattoirs in Wales and Yorkshire.
One of the men was named as Dafydd Raw-Rees, 64, the owner of Farmbox Meats Ltd near Aberystwyth, who was held with a 42-year-old man. A third man, aged 63, was arrested at the Peter Boddy Licensed Slaughterhouse in West Yorkshire. The FSA suspended operations at both sites after raids at the premises on Tuesday on suspicion that the plants sold horsemeat for use in burgers and kebabs.
In a further sign of the severe damage the horsemeat scandal has caused to consumer confidence, 11 of the UK's biggest food suppliers, including Tesco, Asda, Sainsbury's, the Co-operative, the Compass group and Brakes, issued a public letter on Fridayin which they stated they shared food shoppers' "anger and outrage", although the letter stopped short of an apology.
"We are working around the clock to complete the most comprehensive testing of processed beef products ever undertaken, anywhere in the world," it said. "We will do whatever it takes to restore public confidence in the food they buy and eat."
Asda has withdrawn its fresh beef bolognese sauce after tests for horse DNA came back positive. It is the first time since the horsemeat scandal unfolded that horse DNA has been found in fresh produce.
The supplier, Greencore, based in Bristol, also provides beef to Sainsbury's and pork to the Co-operative but both companies are keeping products containing the meat on the shelves.
Asda has removed the Chosen By You 350g Beef Bolognese Sauce from stores across the country along with beef broth soup, meat feast pasta sauces and chili con carne soup, also from Greencore, as a precaution.
Asda said: "As you'd expect, we are withdrawing the beef bolognese sauce from our shelves with immediate effect. In line with the belt-and-braces approach we've taken from the start, we're also withdrawing three other products from the same supplier as a precaution."
Sainsbury's said it would keep two own-brand bolognese sauces supplied by Greencore on its shelves because the meat used by Asda is from Ireland, while its meat is from Britain. It added: "We have already carried out tests on a range of our beef products including burgers, ready meals and minced meat and no trace of horse DNA has been found in any of our products."
The Co-op said products supplied by Greencore were still being sold.
