LONDON (AP) - In Britain, a horse is a horse - not a main course.

Tesco, the country's biggest supermarket chain, took out full-page newspaper ads Thursday to apologize for an unwanted ingredient in some of its hamburgers: horsemeat.

Ten million burgers have been taken off shop shelves after the revelation that beef products from three companies in Ireland and Britain contained horse DNA. Most had only small traces, but one type of burger sold by Tesco was 29 percent horse. The contrite grocer told customers that "we and our supplier have let you down and we apologize."

Reaction to the scandal in Britain goes beyond concerns about contaminated food. While people in some countries happily dine on equine flesh, in the land of Black Beauty and "National Velvet," the idea fills many with horror.

BRITAIN SAYS NEIGH

Labour Party environment spokeswoman Mary Creagh reflected the feelings of many when she said Thursday that eating horsemeat is "strongly culturally taboo in the United Kingdom."

She was echoing prohibitions in Western cultures that go back to 732 A.D., when Pope Gregory III declared horse-eating a pagan practice.

Horsemeat has never been a staple of European diets, but from the mid-19th century it was eaten in countries including Britain as cheap filler food for the poor.

"It tended to be in burgers and potted meats and sausages as cheap supplementary food," said culinary historian Annie Gray. "And it wasn't always labeled, just as we're finding out at the moment."

The sale of horsemeat in the U.K. continued through the 1930s Depression and World War II, when many foods were rationed.

But hippophagy - eating horses - never really caught on in Britain, a land of horse lovers and beef eaters.

"The eating of beef is totally symbolic of being English," Gray said - so horse was always going to be seen as a poor substitute.

VIVA LA DIFFERENCE

Horsemeat is eaten in European countries such as France, Belgium and Italy, as well as by many in China, among the traditionally nomadic people of Central Asia and in parts of Latin America.

In France, specialist horse butchers and supermarkets sell "viande chevaline." There and in Belgium it's popular both cooked and raw, in a form of steak tartare.

Continental journalists have felt the need to explain the context of the Anglo-Irish scandal to readers. An article in 20minutes.fr said the horsemeat discovery had caused a "psychological shock for British consumers, who are no fans of horsemeat butchers." France's Le Figaro newspaper explained that the Irish "are known for their respect of this animal ... and are not in the habit of eating its meat."

Animal-rights campaigners including actress Brigitte Bardot have made little headway against the horsemeat trade, though concerns have arisen over animal welfare. In Belgium, the supermarket chain Lidl stopped selling horsemeat in 2011 after concerns about the treatment of animals by its Latin American suppliers.

Some of the horsemeat eaten in Europe comes from Britain, whose love of horses doesn't stop it sending thousands of horses a year abroad to be killed for meat.

THE HEALTHY ALTERNATIVE?

Fans of horsemeat say it is extremely healthy: low in cholesterol and fat, high in protein and Omega 3 acids.

"I think it's delicious," said Caroline Roddis, a freelance writer who organizes Flogging a Dead Horse, a series of dining events at which horsemeat is served. "It is slightly sweeter than beef and it has got such a good depth of flavor it is hard not to like it."

Roddis reports a healthy interest in her London events, which draw as many as 50 British and foreign diners a night to sample the delights of horseflesh.

She hopes the "horseburger" scandal will make people think more about what they eat.

Officials say the source of the contamination may be a powdered beef-protein additive imported from Spain and the Netherlands to pad out the cheapest burgers, which typically contain between 60 and 70 percent meat alongside flour water and other fillers.

"We don't really think (about) what we are putting in our mouths," Roddis said. "You go to the supermarket and you buy something that looks pinkish and has a label and you don't really think about where it comes from. I think we've really lost touch."

CHANGING TASTES?

The handful of hardy entrepreneurs who sell horsemeat in Britain say the scandal has - paradoxically - been good for business, raising the profile of a meat few had considered.

"We've been very busy the last couple of days," said Paul Webb, director of Exotic Meats, a company in the English Midlands that sells horse burgers, sausages and steaks alongside cuts of crocodile, kangaroo and impala.

He says typical horsemeat buyers are "middle-aged, middle class people who want to try something different."

"We've done some radio phone-ins, and 90 percent of the comments were `I'd try it,'" Webb said.

But not everyone was convinced: "Some people say, `I have a horse, it'd be like eating my grandmother.'"

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