Forget the hounds. As foxes creep in, Britons call the sniper.

Britain has the world’s highest known density of urban foxes, the result of their self-colonization in cities here since the 1930s. There are now more foxes in London than double-decker buses: an estimated 10,000 roam streets and gardens, often in plain view.

Like the raccoons and coyotes that bedevil American city dwellers, foxes mate noisily, leave smelly droppings, dig up flower bulbs, rifle through trash and occasionally attack pets or people. They have been vilified forkilling penguins and flamingo chicks in the London Zoo, and, once, for biting off a baby’s finger.

“They may appear cuddly and romantic, but foxes are also a pest and a menace, particularly in our cities,” Boris Johnson, the mayor of London, said after the finger incident last year. When his own cat appeared to have been mauled by a fox, Mr. Johnson got so angry, he said he wanted to “go out with my .22 and blaze away.”