Operations at Peter Boddy Licensed Slaughterhouse in Todmorden have been suspended by the Food Standards Agency (FSA) after officers visited with West Yorkshire Police.
The plant, at East Hey Head Farm in Hey Head Lane, is believed to have supplied horse carcasses to Farmbox Meats Ltd in Landre, Aberystwyh, which was also raided.
The FSA said the action was taken as part of an investigation into the mislabelling of horse meat, which was sold purporting to be beef for kebabs and burgers.
All meat at both premises was seized along with paperwork, including customer lists from each company. It has not been confirmed what brands and retailers the meat was destined for.
Andrew Rhodes, the FSA’s director of operations, 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.”
Peter Boddy said he will co-operate with Food Standards Agency and denied officers had “raided” his premises.
He said: “It was not a raid – they are welcome to visit whenever they want, they just wanted to see my records, which I will be showing them.”
He added that he does slaughter horses at his plant and that the meat is sold as such in the UK.
Environment Secretary Owen Paterson confirmed it was the first suspected instance of a UK abattoir passing off horse as beef. “This is absolutely shocking,” he said. “It’s totally unacceptable if any business in the UK is defrauding the public by passing off horse meat as beef.
“I expect the full force of the law to be brought down on anyone involved in this kind of activity.”
Mr Paterson earlier met representatives of supermarkets and food suppliers to discuss the growing scandal of horse meat mislabelled as beef.
Joining officials from the FSA, he talked to the Institute of Grocery Distribution, which represents food retailers and suppliers, to discuss plans for a new regime of quarterly testing of products.
Results of tests into the extent of contamination of beef products are expected on Friday.
Mr Paterson will travel to Brussels on Thursday to discuss the scandal with counterparts in EU countries.
Today’s raids came as Waitrose announced it was pulling a range of beef meatballs after tests revealed they might contain pork.
A spokesman said tests on the 480g packs of 16 frozen Essential Waitrose Meatballs had been contradictory but it was removing them from sale as a precaution.
“We have discovered that in two batches of our frozen meatballs produced last summer some of the meatballs may contain some pork,” he said.
“Several tests have been done on this product and, even though the results have been contradictory, we have taken the precautionary action of removing the frozen meatballs from sale and putting up customer information notices in all our branches.
“The meatballs are safe to eat but pork is not listed as an ingredient and should not be part of the recipe.”
Only 480g packs labelled as Best Before End June 2013 and August 2013 are affected, he added.
Supermarket giant Tesco joined frozen food firm Findus and budget retailer Aldi in dropping French supplier Comigel on Monday after discovering a range of spaghetti bolognese ready meals made by the firm contained more than 60 per cent horse meat.
The National Beef Association has suggested the words “United Kingdom origin” should be added to packaging to prevent “further cheating” by European suppliers.
Fraud investigations linked to the horse meat scandal are pointing towards the Continent, the head of food standards in Northern Ireland said.
Gerry McCurdy said the probe into the source of the fraud had still some way to go but it was clear that cost differences between beef and horse meat offered an “extremely helpful financial incentive” for wrongdoing.
“The information available to us does point in the direction of Europe but we cannot be definitive about that at this point in time until those investigations are complete,” he said.
He said 18 countries were involved and negotiations were going on with individual member states of the EU and the European Commission.