Authorities warned the public not to eat beef lasagne sold by the Findus brand
Food retailers have been given a week to test all their beef products after some Findus lasagnes were found to contain 100 percent horsemeat.
The Food Standards Agency (FSA), who ordered the tests, has said it is "very likely" that criminal activity is to blame for the contamination.
While horsemeat does not pose a risk to human health, customers have been told not to eat the Findus beef lasagne in 320g, 360g and 500g sizes.
Findus has apologised to customers and withdrawn the meals from the shelves.
The FSA has now told retailers to test all of their beef products following this latest contamination. The agency has asked for the results to be handed to them by 15 February.
Catherine Brown, chief executive of the FSA, said: "Following our investigations into Findus products, the FSA is now requiring a more robust response from the food industry in order to demonstrate that the food it sells and serves is what it says it is on the label.
"We are demanding that food businesses conduct authenticity tests on all beef products, such as beef burgers, meatballs and lasagne, and provide the results to the FSA. The tests will be for the presence of significant levels of horsemeat."
As well as testing for horsemeat, the FSA is ordering Findus to test the contaminated lasagne for the veterinary drug phenylbutazone, or "bute", as this may have entered the food supply.
The FSA added: "Animals treated with phenylbutazone are not allowed to enter the food chain as [the drug] may pose a risk to human health."
Findus, whose lasagne products are supplied by third-party French firm Comigel, is the latest supplier to be caught up in the horsemeat contamination scandal which has affected companies in France, Ireland, Poland and the UK.
Comigel recently alerted Findus, which supplies to Tesco and Aldi, to withdraw some frozen spaghetti bolognese and lasagne ready-meals because some of the ingredients did "not conform" to the product specification.
A Findus spokesman said in a statement: "All other Findus products have been tested and are not affected. We understand this it is a very sensitive subject for consumers and we would like to reassure you we have reacted immediately. We do not believe this to be a food safety issue.
"We are confident that we have fully resolved this supply chain issue. Fully compliant beef lasagne will be in stores again soon."
Asda recently withdrew four own-brand frozen products supplied by a Northern Ireland company, Freeza Meats, after it was revealed that a batch of meat containing 80 percent horse DNA was found in a cold store operated by the company in Newry.
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