A company whose burgers are sold in fast food restaurants has withdrawn some of its products from sale, after they were found to contain at least 1% horsemeat.
The Food Standards Agency (FSA) said three samples of products made by the Burger Manufacturing Company (BMC) tested positive for horse.
Further tests will reveal exactly how much horse the burgers contained and whether the veterinary drug phenylbutazone, or bute, was present.
A spokesman for the FSA said: "In line with good practice, BMC is withdrawing these products.
"The company is also contacting its customers to inform them of the results of these tests and to recall any of the affected products that they may have."
On its website, BMC lists Sparks Catering Butchers - a wholesaler specialising in the fast food market in the South East - as its largest customer. It also supplies cafes, restaurants and hotels.
The company says it has received "many accolades" for its "high standards and ethics", and insists all its products have "full traceability".
The BMC burgers are the latest products to be withdrawn over the horsemeat scandal.
Some frozen products have been removed from sale by supermarkets including Tesco, Lidl and Iceland, while Nestle has withdrawn two of its chilled pasta meals in Italy and Spain.
Aldi, which also removed some of its products from sale , has been given the all clear after further tests on its range of minced beef and ready meal products.
Sainsbury's said no horsemeat had been found in any of the 250 beef products it tested but said it "will not be complacent".
Meanwhile, the chief executive of Asda, which withdrew an own-brand bolognese sauce and packs of frozen beef burgers earlier this month, admitted trust among consumers had been dented.
"At the end of the day, our customers come into our stores and they expect to buy what's on the label," Andy Clarke said.
"I feel very responsible for that, but I want you to know that I'm leaving no stone unturned to address what happened in our supply chain."
The second stage of the FSA's investigation is expected to finish on Friday.
More than 100 ready meals, including lasagne, chilli con carne, cottage pie and ravioli, are being checked for horse and pork DNA.