Criminal activity is “highly likely” to be to blame after some Findus beef lasagnes were found to contain 100% horsemeat.

Consumers have been warned not to eat the meals and the Food Standards Agency (FSA) has ordered all food companies to test their beef products and provide the results by February 15.

Findus analysed 18 of its beef lasagne meals and found 11 contained between 60% and 100% horsemeat, the FSA said.

But the agency said there is no evidence to suggest the contamination is a food safety risk.

It also confirmed tests have been ordered on the lasagne for the veterinary drug phenylbutazone or “bute”, which is banned from entering the food chain.

Findus has apologised to customers and said refunds would be offered to anyone who bought the affected products, which were made by French food supplier Comigel.

Catherine Brown, chief executive of the FSA, said she believed criminal or fraudulent activity is behind the contamination.

A Findus UK spokesman said: “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.

“We would like to take this opportunity to apologise to our customers for any inconvenience caused.”

Findus UK withdrew its 320g, 360g and 500g lasagne meals from supermarket shelves as a precautionary measure earlier this week.

It came after Comigel alerted Findus and Aldi that their ready meals “do not conform to specification”.

It advised them to remove Findus beef lasagne and Aldi’s Today’s Special frozen beef lasagne and Today’s Special frozen spaghetti bolognese.

Shadow environment Secretary Mary Creagh warned people to be careful about what they are eating.

“I also think we need to get into the schools, hospitals, catering establishments, find out what’s in the freezers and test those as well. We have to have confidence that what we are eating is safe,” she told.

Tesco has also decided to withdraw its Everyday Value spaghetti bolognese, which is produced at the same Comigel site.

A spokesman said: “We are aware of the results of the Findus tests and we will of course assist Findus with their recall process.

“Tests on our frozen Everyday Value spaghetti bolognese product are ongoing under our new DNA testing programme. We will inform our customers of the results as soon as possible.”

The FSA, Defra and the Department of Health are working with businesses and trade bodies to enforce food safety and assess whether there are significant levels of improperly described meat in a whole series of processed beef products in the UK, including supplies to schools and hospitals.

Environment Secretary Owen Paterson said: “The presence of unauthorised ingredients cannot be tolerated … the responsibility and for the safety and authenticity of food lies with those who produce it, and who sell or provide it to the final consumer.”

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