Blaming continental Europe for the horsemeat scandal appeared to backfire on British food chiefs after police raided and closed a slaughterhouse in northern England and a meat processing company in Wales on Tuesday night.
The two firms are suspected of selling horse carcasses which were used in beefburgers and kebabs.
It is the first time British food suppliers have been implicated in the scandal that has forced beef products off the country’s supermarket shelves.
British Environment Secretary Owen Paterson promised the investigation would be “relentless”.
“It is absolutely shocking that we actually have found this practice happening in the UK. This is the first incident. We will be following it up with the full rigour of investigative powers invested in the Food Standards Agency,” he said.
Earlier, two Romanian slaughterhouses emerged as the alleged source of the horsemeat, sold on to other European food producers.
But one of the Romanian firms – CarmOlimp – has defended its practices.
“In 2012, our company on three occasions exported horsemeat to Holland, that was three trucks, a total of 60 tons of meat. This meat was sold as horsemeat, at a price which clearly indicated that it was horsemeat. Our partner had asked for horsemeat and received, along with all necessary documentation, horsemeat,” said General Manager Paul Soneriu.
Ministers from several European countries caught up in the affair are meeting in Brussels today.
The results of UK wide tests on all processed beef products are due to be released on Friday.