LONDON — The British don’t celebrate Thanksgiving, of course, but they have enthusiastically embraced another great American holiday tradition: Black Friday. A little too enthusiastically, it seems. Now, some retailers are even trying to dial back some of the frenzy they unleashed just a few years after introducing the whole idea.

That is because, for a nation that prides itself on its decorous behavior, last year was ugly. Or, what in America is called a typical Black Friday.

At one flagship Asda store in northwest London, part of a retail chain owned by Walmart, one young woman was seen on the floor, desperately clinging to a 40-inch discounted television as several teenagers tried to grab it away.

In Middleton, in Greater Manchester, 200 shoppers barricaded themselves in a Tesco store demanding the promised sale goods, even after all the stock had been depleted.