LONDON — A growing food-contamination scandal in Britain widened into a criminal investigation Friday, with consumers worried about finding horse meat in their burgers or lasagna.

What began as the discovery of traces of horse meat in uncooked burgers labeled as beef last month escalated this week with the announcement that thousands of packages of frozen beef lasagna were being pulled from supermarket shelves because they were potentially tainted as well.

Britain’s Food Standards Agency said the Findus company found at least 60 percent horse meat in 11 of 18 lasagna products that it tested; the meat in at least one of those was entirely horse.

There have been no reports of illness because of the contamination. The standards agency has demanded that the food industry conduct tests on all processed beef products, with the results to be submitted next week.

“The evidence we have about the two cases, of the significant amount of horse meat in burgers and lasagna, points to either gross negligence or deliberate contamination in the food chain. This is why we have already involved the police, both here and in Europe,” the agency said in a statement Friday.

In addition to Britain, horse meat has been detected in beef products sold in Ireland and Sweden.

Officials insist that the issue is not one of safety but rather of false advertising and potential fraud. However, authorities are trying to determine whether an anti-inflammatory drug used to treat horses may be present in the tainted products.

“People have been asking whether it is safe to eat any frozen meat products at the moment. There is no reason to suspect that there’s any health issue with frozen food in general, and we wouldn’t advise people to stop eating it,” the Food Standards Agency said.

Horse meat is regularly consumed in some European countries, including France and Italy. But Britons generally object to the idea of horse on the menu, and the scandal is dominating headlines, with Prime Minister David Cameron’s office describing the revelations as “very distasteful.”

“This isn’t really about food safety. It’s about effective food labeling. It’s about proper retail practice,” Cameron said Friday at an unrelated summit of European Union leaders in Brussels. “And people will be very angry to find out they have been eating horse when they thought they were eating beef.”

• Henry Chu, MCT Campus