The video, shot from a passing bus and lasting barely a minute, is harrowing. A powerful young dog bites an 11-year-old girl in front of a grocery store in Birmingham, England. As pedestrians scatter in terror, the dog chases a man into a gas station plaza, pulling him down repeatedly, its jaws clamped on the man’s arm and shoulder, as he tries desperately to shake off the animal.

Posted on social media last week, the footage inflamed a debate in Britain over the American bully XL, a relatively new dog breed that has become highly popular, even as it has been blamed for a string of dangerous attacks. Activists claim the animals are responsible for more than 40 percent of all dog attacks in the country and a disproportionate number of fatalities.

On Friday, after yet another attack killed a man, Prime Minister Rishi Sunak branded the bully XL a “danger to our communities” and said his government would take steps to ban it “so we can end these violent attacks and keep people safe.”

It is a replay, three decades later, of the war over pit bulls, which raged in Britain and the United States, though with different results. Pit bulls, from which the bully XL is likely descended, were outlawed in Britain but remain mostly legal in the United States, even if some cities impose restrictions on them.

Now, as then, there is a pitched battle between those who say some dogs are bred to be killers and those who say no dog is born that way. Now, as then, there is a social and class element, given the popularity of these dogs in poorer neighborhoods, often with members of gangs. Now, as then, the scientific data on the propensity of certain breeds to attack humans is frustratingly inconclusive.

Even the British political cycle is oddly parallel: a Conservative government, unpopular after a long stint in power, is seizing on an emotive issue to appeal to weary voters. Britain banned pit bulls, along with three other breeds, in 1991, at a time when Prime Minister John Major was facing a difficult campaign against the opposition Labour Party (the Tories pulled off a narrow victory the following year).

Still, the recent spate of attacks — which have been highlighted by an advocacy group, Bully Watch, that has posted daily reports and video of attacks on social media — has propelled the issue beyond mere partisanship.

The Labour leader, Keir Starmer, said this week that “nobody should feel comfortable” with the images from Birmingham. On Thursday, a 52-year-old man, Ian Price, died in Stonnall, a village in Staffordshire, after being mauled by two suspected bully XLs. The police arrested their 30-year-old male owner.

Mr. Starmer said there was a strong case for banning bully XLs, a muscular, powerfully built dog that stands between 21 and 23 inches and weighs up to 130 pounds. “Clearly,” he said, “something needs to change.”

There is little scientific data on the behavior of the bully XL, however, partly because it has only existed since the late 1980s. Experts say it is likely to have been crossbred from other dogs in the pit bull terrier family, some imported from the United States.

Critics argue that outlawing the bully XL or any other breed will not reduce serious or fatal dog attacks. They point out that the passage of the Dangerous Dogs Act in 1991 has not prevented the number of dog bites, or fatal attacks, from rising in Britain. The British Veterinary Association and animal-rights groups oppose bans on the grounds that they are unjust, in addition to being ineffective.

Yet proponents of a ban argue that a sudden spike in fatalities, many of which were caused by bully XLs, demonstrates the need for further action. Between 2001 and 2021, three people in Britain died each year, on average, as a result of a dog attack, according to the Office for National Statistics. Last year, 10 people died, while seven people have died so far this year.

To the activists who run Bully Watch, the government has already waited too long to act. The group’s founders have chosen to remain anonymous, saying they would be subjected to reprisals from dog breeders. They have created their own database of attacks, using Facebook and other social media, which documents 351 cases of attacks by large bully breeds this year. Since 2021, they say, bully XLs have been responsible for 11 confirmed, and 3 suspected, deaths.

The emergence of the bully XL, however, illustrates the futility of banning specific breeds, according to critics. They argue that dog owners will simply continue mixing dogs to create new breeds. In addition to the pit bull, Britain has banned the Japanese Tosa, the Dogo Argentino and the Fila Brasileiro — animals that have either been bred as fighting dogs or are known for their aggression.

Bronwen Dickey, an American author whose book “Pit Bull: The Battle over an American Icon,” explored the history of the breed as well as the outcry in the 1990s, likened bans to former President Donald J. Trump’s plan to halt the influx of immigrants across the southern border of the United States.

“It’s very much like people who say, ‘build the wall,’” Ms. Dickey said. “Squint and it may seem like a reasonable solution, but then it doesn’t actually work.”

The alternative, she and other critics said, is to better regulate the dog-breeding industry, particularly so-called backyard breeders, who often breed animals in grim conditions and treat them cruelly to make them more aggressive.

Adding a new breed to the banned list is not straightforward. The American bully comes in various sizes, from pocket to XL, attesting to how protean the breeding process can be. Owners often resist authorities who try to take away their dogs, disputing its breed.

“How do you legislate against those dogs when you can’t even identify which is a pit bull?” said Carri Westgarth, chair of human-animal interaction at the University of Liverpool.

Mr. Sunak conceded the murky lineage of the bully XL. He said the government would consult experts to define the breed before adding it to the list of outlawed dogs. In Britain, the police can confiscate an illegal dog and a court can later order it destroyed.

Another difficulty with singling out a breed, Professor Westgarth said, is that it implies other dogs are not also capable of biting humans. French bulldogs, Shih Tzus, and Jack Russell terriers rank high on the list of dogs with incidents of bites, but she added, “Bull breeds will do more damage than your Chihuahua.”

There is also a social and economic undercurrent. When the government set out to ban pit bulls in 1991, the Home secretary at the time, Kenneth Baker, examined data on dog bites and discovered that Alsatians and other breeds favored by upscale owners might also qualify for the blacklist.

“This would have infuriated the ‘green welly’ brigade,” he wrote in his 1993 memoir, referring to the people who wear Wellingtons as they walk with their hounds in the Cotswolds or other country retreats.

“The ‘pit bull lobby’ came to my aid,” Mr. Baker continued, “appearing in front of TV cameras with owners usually sporting tattoos and earrings while extolling the allegedly gentle nature of their dogs, whose names were invariably Tyson, Gripper, Killer, or Sykes.”

That dynamic exists with bully XLs, though social media has added a new element. The breed has been popularized by owners who are influencers on Instagram and YouTube; some focus obsessively on genealogy. Half of all bully XLs in Britain “descend from one inbred animal from the U.S. named Killer Kimbo,” the Daily Mail reported, citing research compiled by Bully Watch.

In an interview on Thursday, one of Bully Watch’s three organizers said he and his colleagues recognized there was a danger that the debate over these dogs could become “radicalized.” He said they had decided to stop posting every reported incident of an attack and would wait to see how the government responded.

Hours later came the attack on Mr. Price, and on Friday morning, Mr. Sunak’s pledge to ban the dogs responsible. “For Jack Lis,” Bully Watch posted, referring to a 10-year-old boy who was killed by a bully XL in 2021, as well as a roll-call of other victims, “A ban is a step in the right direction.”