Test results for horse meat in British processed meals are due as detectives continue questioning three men arrested in connection with the mis-labelling scandal.
The Food Standards Agency (FSA) will report on the UK products after asking retailers and suppliers to provide "meaningful results" from tests to detect the presence of horse meat in processed meals labelled as beef. The FSA said it wanted the food industry to show the food it sells and serves is what it says it is on the label.
The test results, for significant levels of horse meat, will come from all beef products such as burgers, meatballs and lasagne.
Prime Minister David Cameron reportedly believes supermarkets have been too silent on the scandal. A senior No10 source told the Daily Telegraph: "It is not acceptable for retailers to remain silent while their customers have been misled. The supermarkets need to justify their action and reassure the public."
The eagerly-awaited test results will emerge as police in Wales probe three men arrested on suspicion of offences under the Fraud Act. The trio were taken into custody from two plants inspected and temporarily shut down by the FSA on Tuesday.
Sources said Dafydd Raw-Rees, 64, owner of Farmbox Meats near Aberystwyth, was arrested along with a 42-year-old man. A 63-year-old man was also arrested on suspicion of the same offence at Peter Boddy Slaughterhouse in Todmorden, West Yorkshire.
On Wednesday, owner Mr Boddy, 63, said he had done nothing wrong and insisted the FSA inspection was merely to look at his records, but was on Thursday night unavailable for comment. His firm is also contracted to remove fatally injured horses from the Grand National. It said it was "confident" no unfit meat had entered the food chain.
The arrests were made by Dyfed-Powys Police in a joint operation with the FSA. The two plants became the first UK suppliers suspected of passing off horse meat for beef. Production at both plants was suspended pending the outcome of investigations into claims they supplied and used horse carcasses in meat products purporting to be beef for burgers and kebabs.
The FSA said on Tuesday it had "detained" all meat found at the premises and seized paperwork and customer lists from the two companies. The arrests were made as Asda withdrew its 500g beef bolognese sauce from shelves after tests revealed the presence of horse DNA, the supermarket chain said. The company apologised to customers and said it was taking a "belt-and-braces approach" by removing a further three beef products made by the same supplier, the Greencore plant in Bristol, as a precaution.
On Thursday it emerged a significant amount of horse meat containing the painkiller phenylbutazone - or "bute" - could have been entering the food chain for some time. Authorities in Britain and France are trying to trace the carcasses of six horses contaminated with bute - which were slaughtered in a UK abattoir and may have entered the human food chain across the Channel.