An alpaca condemned to death after testing positive for bovine tuberculosis looks set to die despite his owner pleading with Boris Johnson for a stay of execution.

Geronimo the six-year-old alpaca has tested positive for the disease twice and a High Court judge has ruled he must be put down.

His owner, Helen Macdonald, whose farm is in Wickwar, South Gloucestershire, said she will “stand in the way of any gunman who comes to destroy Geronimo” as she disputes the test results.

More than 80,000 people have signed a petition asking the prime minister to step in, while nearly £19,000 has been donated towards legal costs.

But Boris Johnson’s spokesman said the rules need to apply equally and also defended the tests, saying there were no plans to carry out further tests.

“The test used on Geronimo is highly specific, it is validated, it is reliable and the risk of a false positive is extremely low,” he said.

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“A retest after two consecutive positive test results wouldn’t invalidate the previous tests.

“So, there’s no plans for any further tests.

“We recognise how distressing this clearly is for Ms Macdonald, as it is for farmers who have had to put cattle down – 27,000 had to be put down last year alone.

“We need disease control measures to be applied consistently if we are able to tackle it and obviously that’s why we need to move ahead now.

“We have done these highly accurate tests and we’ve no plans to change that.”

Environment Secretary George Eustice said Geronimo was tested “using a highly specific and reliable test”.

But Ms Macdonald, a veterinary nurse and alpaca breeder, said: “It’s a total load of lies, the testing has never been validated.

“He’s still standing by such a ridiculous claim because they’ve made errors of judgment and they’ve been caught out.

“If he’s willing to kill a healthy animal in front of the whole world without testing him properly first, then it’s a sorry state of affairs.

“And it will be for the world to see. Because if he sends some poor person down here with a gun to shoot Geronimo then it will get filmed by the world’s media.”

The owner, 50, said the government has known “since 2016 that those tests produce false positives if you give an alpaca more than two shots of tuberculin within a 12-month period”.

Geronimo had four skin tests before he was exported from New Zealand, which were all negative.

He then had two blood tests and a skin test in the UK that were positive.

The Department for Environment, Food and Rural Affairs (Defra) said the test has a 0.36% chance of producing a false positive. However, no trials for how accurate the tests are on alpacas have been carried out.

Defra has refused to test the other five alpacas Geronimo lives with.

Ms Macdonald has been embroiled in a legal battle with Defra since 2017 but the case has gained traction after a second death warrant came into effect on Thursday after a final High Court bid to save him failed.