LONDON — Few things divide British eating habits from those of Continental Europe as clearly as a distaste for consuming horse meat, so news that many Britons have unknowingly done so has prompted alarm among shoppers and plunged the country’s food industry into crisis.

A trickle of discoveries of horse meat in hamburgers, starting in Ireland last month, has turned into a steady stream of revelations, including, on Friday, that lasagna labeled beef from one international distributor of frozen food, Findus, contained in some cases 100 percent horse meat.

The widening scandal has now touched producers and potentially millions of consumers in at least five countries — Ireland, Britain, Poland, France and Sweden — and raised questions of food safety and oversight, as well as the possibility of outright fraud in an industry with a history of grave, if episodic, lapses despite similarly episodic efforts at stricter regulation and reform. Already, tens of millions of hamburgers from several suppliers have been recalled.

The growing scale of the problem became clear this week when the chief executive of the Food Safety Authority of Ireland, Alan Reilly, said that meat was being deliberately mislabeled. “We are no longer talking about trace amounts,” he told RTE, the national broadcaster. “We are talking about horse meat. Somebody, someplace, is drip-feeding horse meat into the burger manufacturing industry. We don’t know exactly where this is happening.”