Police have been urged to launch an investigation into the growing horse meat scandal after lasagne emerged as the latest contaminated product.
Ministers were accused of "sleeping on the job" after the Food Standards Agency said it was "highly likely" that criminals were to blame.
It comes after tests found some Findus beef lasagnes contained up to 100% horse meat. Food companies have been ordered to carry out urgent tests on all of their beef products.
Traces of horse meat were first spotted in beef burgers sold by Tesco last month.
Mary Creagh, Labour's shadow environment secretary, said: "The Irish Government has called in the police and fraud experts to investigate the horse meat fraud, yet complacent British ministers have not and are asleep on the job.
"The latest revelations raise questions about the extent of this scandal - this is no longer just a food safety issue but possibly a criminal trade.
"The public must have confidence that the food they buy is properly labelled, legal and safe to eat, whether it is purchased from a supermarket or in a school canteen."
Speaking on the BBC's Today programme, she added: "The big concern for me now is corner shops, schools, hospitals, prisons, public-sector caterers, people who may have these products sitting in their fridges and freezers."
Her Labour colleague Tom Watson questioned why police were not already investigating the scandal.
The Food Standards Agency said there was no evidence of a safety risk. But tests are underway to see whether a banned veterinary drug was contained in the meat, and customers have been advised not to eat it.
Phenylbutazone, or 'bute', is banned from entering the food chain.
Catherine Brown, chief executive of the FSA, said: "This is an appalling situation.
"I have to say that that the two cases of gross contamination that we see here indicates that it is highly likely there has been criminal and fraudulent activity involved."
She added: "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 horse meat."
The chair of the House of Commons Environment, Food and Rural Affairs Committee, Anne McIntosh, said: "I think the message is to go out and buy your food as locally as you can so you know where the beef is coming from."
Findus UK tested 18 of its beef lasagne products and found 11 contained in the range of 60% to 100% horse meat, the FSA said. Lasagnes were withdrawn from supermarket shelves earlier this week.
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."
Tesco and Aldi have withdrawn a range of ready meals poduced by the same French supplier, Comigel.