Beef products have been removed from the shelves of a UK supermarket after they were labelled as British but came from South America and Europe.
The National Food Crime Unit (NFCU) is investigating the potential food fraud, which involves pre-packed and deli products.
The supermarket and supplier have not been publicly named.
Tesco, Sainsbury's, Asda, Aldi, Lidl, the Co-op, Waitrose, Morrisons, Iceland, Marks & Spencer told the BBC they are not the retailer that had been supplied with the meat.
Ocado separately told The Mirror they are not the supermarket in question.
Farmers Weekly claims the investigation involves the review of about 1.3 million documents with products being sold to customers as "best British beef".
Andrew Quinn, deputy head of the NFCU, said: "The retailer was notified on the same day that we took action against the food business suspected of the fraud and immediately removed all affected products from their shelves.
"The retailer continues to work closely and co-operatively with the NFCU investigation to progress the case against the supplier. This is not a food safety issue but a matter of food fraud.
"Any fraud investigations of this nature take time to go through evidence and bring to any outcome, including any potential prosecution.
"We take food fraud very seriously and are acting urgently to protect the consumer."
It comes ten years after horsemeat was discovered in the food supply chain in 2013, with products being sold as beef.
Millions of products were withdrawn all over Europe as a result.
At the National Farmers' Union (NFU) conference last month, president Minette Batters warned against the possibility of another food scandal, saying: "Ten years on from the horsegate scandal, we cannot afford to be so complacent about the risks that continue to exist."
Labour has said there are "very serious questions to answer" about how a UK supermarket has become embroiled in a major beef fraud investigation.
Shadow environment secretary Jim McMahon said: "We were told the lessons of the horsemeat scandal had been learnt, but unfortunately this investigation could cast that into doubt.
"There are clearly very serious questions to answer and it's right that an urgent investigation is currently under way."
A spokesman for the Association of Independent Meat Suppliers, said: "It is only today that we have found the product concerned is beef, and it is our belief, given the popularity of sliced cooked beef across all trade channels, that its sale by food fraudsters will not have been limited to a single supermarket.
"The NFCU's current play book has the potential to damage UK overseas trade simply by their policy of a lack of transparency and industry engagement."
