Four years ago, Geronimo was just another handsome alpaca from New Zealand on the cusp of a new low-key life in the British countryside.

Though he has barely strayed from the same corner of a farm in Gloucestershire since then, he is now arguably the most divisive alpaca in Europe. The question of whether he should be executed is now pitting British public figures, veterinarians and bovine experts against one another.

The British Department for Environment, Food and Rural Affairs, known as Defra, says that 8-year-old Geronimo has bovine tuberculosis — “one of the greatest animal health threats we face today,” as a spokesperson called it in a statement Tuesday — and therefore authorities need to “cull” him.

Geronimo’s owner, Helen Macdonald, and the dozens of “alpaca angels” — who have showed up at her farm over the past few days to take shifts and guard him from executioners — maintain that he is perfectly healthy. It is the bovine tuberculosis testing system that is flawed, Ms. Macdonald, who is a veterinary nurse, insists.

Though the British authorities have a warrant to show up to kill Geronimo any time in the next 24 days, Ms. Macdonald said, she and her new alpaca-loving friends are determined to thwart their plans.

“They are here to protect him and form a human chain,” she said of the “alpaca angels” in an interview on Tuesday.

More than 100,000 people have signed a petition offering Ms. Macdonald support and asking Prime Minister Boris Johnson and other politicians to save Geronimo and more broadly, protect “all camelids” — the term for slender-necked animals including alpacas, llamas and camels — from the TB tests, which supporters say produce false positives.

Mr. Johnson’s father, Stanley Johnson, made headlines on Monday for offering his support, writing in The Sun that he hoped Ms. Macdonald and her supporters would “block the men from Defra from carrying out their absurd murderous errand.” On Monday, about 30 people also marched to Downing Street to protest the killing of Geronimo.

Ms. Macdonald is convinced Geronimo is healthy in part because her “cheeky” alpaca has not exhibited any of the symptoms of contagious disease since he first tested positive for bovine TB four years ago. The disease typically causes severe weight loss.

“He’s really quite fat,” she said, adding that his fleece is also extraordinarily soft. “If he was sick, he would not have nice fiber,” she said.

But more than how he looks, it’s other people’s stories about how the test seems to be misleading that has Ms. Macdonald convinced that someone should step in to save Geronimo.

Bob Broadbent, a veterinary surgeon in Gloucestershire who has worked with camelids since 1986, said that he has seen more cases of bovine tuberculosis “than I would care to remember” over the years. He has also been examining Geronimo regularly over the past three years and in his opinion, he said, the test is flawed and Geronimo does not have tuberculosis.

Defra’s bovine tuberculosis test involves more than just a blood test; it requires an injection of “tuberculin” as “a primer” 10 to 30 days before the test, Dr. Broadbent said. He believes that while this may not create problems in cattle, it sometimes creates false positives in alpacas. Essentially, the result is positive because the test detects the tuberculin — not because they actually have tuberculosis.

In a statement, the Environment secretary, George Eustice, countered that Geronimo has tested positive not once but twice, using a “highly specific and reliable test.”

“My own family have a pedigree herd of South Devon cattle and we have lost cows to TB,” he said, “so I know how distressing it can be and have huge sympathy for farmers who suffer loss.”

The chief veterinary officer of the United Kingdom, Christine Middlemiss, echoed Mr. Eustice. The chances of a false positive are significantly less than 1 percent, she said in a statement.

“While I sympathise with Ms. Macdonald’s situation, we need to follow the scientific evidence and cull animals that have tested positive for TB, to minimise spread of this insidious disease, and ultimately to eradicate the biggest threat to animal health in this country,” she wrote.

Over 27,000 cattle in England were slaughtered in the last year to tackle the disease according to Defra, which called the idea that priming could cause a false positive “misleading” in a blog post Monday.

This is the second time that Dr. Broadbent, the veterinary surgeon, has seen this with a local alpaca, he said. In 2018, another farmer was required to test her alpaca after some nearby cattle tested positive for bovine tuberculosis. Only one — Karly — was positive. The owners were highly skeptical because they did not think that Karly had come into contact with the cattle. After euthanizing Karly — which he was required to do by law — he tested her blood.

“She passed the test,” he said. “I am convinced that she did not have TB.”

Bridget Tibbs, Karly’s owner, said that it’s absurd that in order to retest alpacas for TB while they are alive — for example to prove that Geronimo is healthy after all, something that Ms. Macdonald wants to do — farmers need permission from the government.

“The system is killing undiseased animals all over the place,” said Ms. Tibbs, who runs Cotswold Alpacas. “It’s barbaric.”

She called Geronimo, whom she had just visited, a “beautiful, strong, healthy stud male with the girl alpacas on his mind.”

One of the worst aspects of it all, Ms. Macdonald said, is that she wasn’t required to test Geronimo when he first arrived from New Zealand. Rather, she volunteered to do so a few weeks after he arrived because she was trying to promote use of the test, she said.

Over the past several years, as she’s been fighting in court to save Geronimo, he’s been stuck in isolation; he can see some of her other 80 or so alpacas on her 25-acre farm, but she has to keep a fence between them, she said. She believes the government used the test incorrectly the second time around.

Peter Martin, one of the volunteers now spending his days at her farm, said that though Ms. Macdonald lost her court battle, he is determined to protect Geronimo from the authorities.

“We have a plan for when they arrive,” he said. Though the “alpaca angels” did not want to give away all their tactics, he said he’s convinced they are technically legal.