Waitrose knew its beef meatballs might have contained pork two weeks before informing authorities it has emerged as the meat contamination scandal escalates.

The upmarket grocer withdrew batches of beef meatballs, which have since been identified as containing pork, on January 30 and February 4 but did not inform the Food Standards Agency (FSA) until Tuesday.

The grocer said it had been running several rounds of internal tests after receiving “contradictory” results and had not informed the FSA as there was no health risk to consumers, The Guardian reported.

Waitrose said: “Our procedure was also to make an assessment of the number of packs that could possibly still be in customers’ freezers.”

Managing director Mark Price said in an open letter to customers: “We have now done tests on 40 of our meat products, no horse meat was found in any of these tests.

“We did, however, discover that in just two batches of our essential Waitrose frozen British beef meatballs (480g), some of the meatballs may contain some pork. In fact, one of the tests carried out showed that the meat in the meatballs was, as it should be, 100% beef.”

He added: “But because another test indicated there may be some pork, I felt it important for you to be aware.”

Environment minister Owen Paterson met with EU ministers yesterday and agreed to the random testing of meat products for the horse anti-inflammatory drug bute as well as for horse DNA.

Paterson said: “This is a criminal conspiracy to defraud the public. At the beginning of the week we talked about incompetence, it looks as if it has gone beyond incompetence, it now looks as if it is criminal.

“The question is who did what, where, when? I am confident we’ll get to the bottom of this. Investigations are accelerating.”

It emerged yesterday that a Dutch trader involved in the supply of horse meat used in Findus lasagnes had previously been jailed for passing off Argentine horse meat as beef.

The FSA will tomorrow unveil results of thousands of tests on supermarket products for horse meat and bute conducted in independent laboratories.

Morrisons said today sales of fresh meat at the grocer - which has not been implicated in the scandal - have risen 18% while sales of fresh burgers rose 50% since the crisis took hold almost a month ago.

Chief executive Dalton Philips said: “There’s never been a better time for consumers to buy fresh meat from sources they know they can trust.  Because we work direct with farms, (even owning our very own), our counters and expert staff can confidently offer the most reliable meat to customers. 

“Shoppers who are concerned by the recent crisis should buy fresh meat supplies from a trained butcher. We encourage all customers to talk to the butcher about where their animals are sourced from. Buying from reputable, skilled butchers should give shoppers reassurance and greater confidence in meat products.”