British officials and police raided two meat plants on Tuesday as part of investigations into a Europe-wide scandal over the labelling of horsemeat as beef, the Food Standards Agency said.
"The agency and the police are looking into the circumstances through which meat products, purporting to be beef for kebabs and burgers, were sold when they were in fact horse," the agency said.
The agency suspended operations at the two places, a slaughterhouse in Todmorden, northern England and a meat producing factory in Aberystwyth, west Wales, it said in a statement.
The FSA said it believed that the Peter Boddy slaughterhouse in Todmorden, in the county of West Yorkshire, supplied horse carcasses to Farmbox Meats in Aberystwyth.
Officials seized all meat found at the two premises as well as paperwork including customer lists.
Andrew Rhodes, director of operations at the FSA, said: "I ordered an audit of all horse producing abattoirs in the UK after this issue first arose last month and I was shocked to uncover what appears to be a blatant misleading of consumers.
"I have suspended both plants immediately while our investigations continue."
Environment Secretary Owen Paterson said in the statement that the development was "absolutely shocking."
"It’s totally unacceptable if any business in the UK is defrauding the public by passing off horsemeat as beef. I expect the full force of the law to be brought down on anyone involved in this kind of activity," he said.