Tests on beef lasagne have revealed that some of the ready meals were made entirely from horsemeat.
Findus analysed 18 of its beef lasagne products and found 11 meals contained between 60% and 100% horsemeat, the Food Standards Agency (FSA) said.
There is no evidence to suggest the horsemeat found in the Findus beef lasagne is a food safety risk, the FSA said.
However, the agency has ordered urgent tests on the lasagne for the veterinary drug phenylbutazone. Meat from animals treated with “bute” is not allowed to enter the food chain in Britain as it may pose a risk to human health.
All food companies have been told to test their beef products, with the FSA saying it was “highly likely” that criminal activity was to blame for the contamination.
Consumers who have purchased the ready meals – produced by French food supplier Comigel on behalf of Findus – have been advised by the FSA not to eat them and return them to the shop they were bought from.
Retail giant Tesco and discount chain Aldi have already withdrawn a range of ready meals produced by Comigel over fears they contained contaminated meat.
Findus UK has already started a full recall of its lasagne products. It 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 products “do not conform to specification”.
Findus UK apologised to customers “for any inconvenience caused” – and said anyone who bought the affected lasagne products could get a full refund.
A spokesman said: “We understand this 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 have had three weeks of damaging revelations about what is happening in the meat industry … there is evidence that criminal gangs are involved in this, and frankly I cannot believe that the Government hasn’t called in the police to investigate this in the UK.
“I don’t see how we get to the bottom of it without getting in specialist teams and working out who is behind this fraud and why it is happening.”
People must have confidence that the food they buy is properly labelled, legal and safe to eat, she added.