LONDON (REUTERS) - An eight-year-old alpaca named Geronimo, who was at the centre of a legal row with the British government and whose plight triggered a nationwide campaign to keep him alive, has been killed after twice testing positive for bovine tuberculosis.

Video footage showed veterinary staff in blue overalls, masks, and goggles, backed by police officers, arrive at a farm in western England where the animal lived, and lead him away.

The order to kill the alpaca led to pleas from owner Helen Macdonald for British Prime Minister Boris Johnson and his wife Carrie to show mercy, prompting some celebrities to demand the PM swerve away from what they cast as a public relations disaster.

Protesters in recent weeks had shown up at Macdonald's farm to guard him from executioners after the government ordered him to be put down. More than 140,000 people had signed a petition calling for the creature to be saved.

"The infected animal was moved from the premises and euthanised by staff from the Animal and Plant Health Agency (APHA) as a necessary measure to control the spread of bovine tuberculosis," the Department for Environment, Food and Rural Affairs said in a statement.

Bovine tuberculosis is a chronic bacterial disease of cattle that occasionally affects other mammal species. It can spread to humans through the ingestion of unpasteurised milk.

Macdonald, a veterinary nurse, said the alpaca was negative when he was brought in from New Zealand and believes the government's diagnosis is the result of a false positive. She has spent thousands of pounds on a failed court battle to save the animal.

A spokesman for the prime minister said it is highly distressing for someone to lose an animal.

"Our sympathies are with Ms Macdonald and others that are affected by this terrible disease," he said.