Two leading UK catering firms have announced the withdrawal of frozen beef products after horse DNA was found.
Sodexo, which supplies food to schools, care homes and the Armed Forces, said beef had been pulled from its UK sites "with immediate effect".
The firm said despite "repeated guarantees" from suppliers, its checks had uncovered a frozen beef product that tested positive for equine DNA.
Another firm, Scotland Excel, which works mainly with councils, said it advised customers to stop using stocks of frozen burgers after horse DNA was found in a frozen beefburger at North Lanarkshire Council.
The company, which named Brakes as their supplier, stressed the move was a precaution.
Sodexo said its Tillery Valley Foods business, which supplies meals to the healthcare sector, was not affected.
A spokeswoman would not confirm which of its sites had been supplied with the frozen products. Catering at Ascot Racecourse, which hosts Royal Ascot, attended each year by the Queen, is run by Sodexo Prestige, according to the firm's website.
The spokeswoman also declined to name the supplier of the beef products which tested positive for horse DNA and would not say if it was a British or Irish manufacturer.
It comes hours after the owner of Birds Eye recalled ready meals from shelves in four countries.
They were made by supplier Frigilunch NV, which also produces a branded chilli con carne sold in Belgium that has tested positive for traces of horsemeat.
Birds Eye said: "We want to reassure you from the testing we have completed that all Birds Eye beef burgers, beef pies and beef platters do not contain horse DNA.
"Whilst this is not a food safety issue, it is clearly unacceptable. In accordance with our high standards, we are immediately withdrawing this product from sale in Belgium."
Iglo Foods Group, the parent company of Birds Eye, said in addition to the three product recalls in Britain and the same meals in Ireland, it was withdrawing eight products in Belgium and one in the Netherlands.
The Continental food recall also affects ox tongue, mince, meat balls and hamburgers.
In recent weeks it has emerged European meat supply chains had been contaminated with horsemeat, which forced a number of British supermarkets to recall products.
The France-based Findus food company has also been hit by the scandal.
The Birds Eye revelation comes after it initiated a Europe-wide testing programme for horse DNA of its suppliers and on its finished beef products.
Environment Secretary Owen Paterson said: "It's unacceptable for any products to be marked as beef, when they also contain horse meat. Thankfully these results show that the vast majority of products on our shelves match what's on the label.
"Food businesses from throughout the industry, including retailers, manufacturers, caterers and other wholesalers, are putting enormous effort into getting this testing completed as quickly as possible. It's an important first step from them in rebuilding the certainty and trust that consumers deserve."
The Food Standards Agency (FSA) released the latest tranche of test results submitted by the food industry earlier. They showed that out of 1,133 meat products checked, only six - including Sodexo's - were positive for horse.
Results of industry tests on 2,501 beef products collated by the FSA last week revealed 29 positive results, relating to Aldi's special frozen beef lasagne and special frozen spaghetti bolognese, Co-op frozen quarter-pounder burgers, Findus beef lasagne, Rangeland's catering burger products, and Tesco Value frozen burgers and Value spaghetti bolognese.
The FSA said no tests to date on samples containing horse DNA have found the veterinary drug phenylbutazone, or bute, to be present.
Retailers have completed about 90% of their tests so far, while manufacturers, caterers and wholesalers have completed about 80% of their tests, according to the FSA. Further test results are due next Friday.