People need to be told officially whether they should eat any processed beef foods in the wake of the discovery of horsemeat in Findus lasagne, the shadow environment secretary has said.
Labour's Mary Creagh accused ministers of "pretending this isn't happening".
The government said it was working with businesses to enforce regulations.
The Food Standards Agency has ordered UK retailers to test all processed beef products. Findus has withdrawn its lasagne from sale.
It is the latest company to be caught up in the controversy surrounding contamination of meat products, which has affected companies in the UK, Irish Republic, Poland and France.
Last month, Irish food inspectors announced they had found horsemeat in some burgers stocked by a number of UK supermarket chains, including Tesco, Iceland and Lidl.
'Criminality or negligence'
Ms Creagh expressed fears that there were further revelations to come from the food industry.
"What we have had over the last four weeks is a constant drip, drip, drip of revelations from the food industry, from the Food Standards Agency, and what I am worried about is that the more they are testing for horse, the more they are finding," she said.
She suggested official guidance was needed on whether people should eat other processed foods labelled as containing beef.
"I certainly wouldn't, but I'm waiting for the government, the experts, the scientists, to tell us and issue proper clear advice for consumers," she said.
"It's simply not good enough for ministers to sit at their desks and pretend this isn't happening."
Environment Secretary Owen Paterson called the Findus discovery "completely unacceptable" and said the presence of unauthorised ingredients in foods "cannot be tolerated".
Mr Paterson said the government was working closely with businesses to "root out any illegal activity" and enforce regulations.
"Consumers can be confident that we will take whatever action we consider necessary if we discover evidence of criminality or negligence," he said.
The FSA said it was "highly likely" criminal activity was to blame for the contamination.
Chief executive Catherine Brown told the BBC: "I have to say 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.
"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."
The agency has asked for test results by next Friday.
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We understand this is a very sensitive subject for consumers”
The FSA said there was no evidence of a health risk from the contaminated lasagne, but has also ordered Findus to test the products for the veterinary drug phenylbutazone, or "bute".
"Animals treated with phenylbutazone are not allowed to enter the food chain as [the drug] may pose a risk to human health," it said.
Findus's affected products were made by a third-party French supplier, Comigel, which had alerted the company to concerns that the beef lasagne product did not "conform to specification".
The FSA said Findus had tested 18 of its beef lasagne products and found 11 meals containing between 60% and 100% horsemeat.
Findus had withdrawn its beef lasagne in 320g, 360g and 500g sizes as a precaution on Monday.
The company 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. We would like to take this opportunity to apologise to our customers for any inconvenience caused."
It said all its other products had been tested and were not affected.
A statement from the British Meat Processors Association (BMPA) said it "deplores the latest reported incidents of gross contamination of some processed meat products".
"The BMPA has urged its members to be vigilant, and to review their raw material and ingredients-sourcing procedures in order to ensure that they meet their responsibilities to produce safe food and to describe and label their products accurately."
Earlier this week, Comigel had advised Findus and Aldi to withdraw Findus Beef Lasagne and Aldi's Today's Special Frozen Beef Lasagne and Today's Special Frozen Spaghetti Bolognese.
An Aldi spokesman said its products had been withdrawn immediately and the retailer was carrying out its own investigations.
"The products will remain withdrawn from sale until we are confident that the meat content complies with the specification presented to us," he said, adding that customers could claim refunds by returning packaged products.
Tesco also decided to withdraw Everyday Value Spaghetti Bolognese.
The Tesco product was produced at the same Comigel site but there was no evidence of contamination, the supermarket said.
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