The UK government acted unlawfully by discharging elderly hospital patients into care homes in the early stages of the coronavirus pandemic, where many died, two judges ruled on Wednesday.
Policies in place as the virus took hold in Britain in early 2020 failed to take into account the risk to elderly and vulnerable residents from asymptomatic transmission, said the High Court judges.
Prime Minister Boris Johnson's government has been repeatedly criticised for its initial response to the global health crisis.
In October last year, lawmakers concluded that "many thousands of deaths" could have been avoided had elderly patients been tested before they were discharged into care homes.
Johnson's former chief aide, Dominic Cummings, has even accused the then health secretary Matt Hancock of having lied to colleagues that patients were tested.
Wednesday's ruling at the High Court in London came in a case brought against Hancock and Public Health England by two women whose fathers died from Covid-19.
Evidence from policy documents in March and early April 2020 showed that the government "simply failed to take into account the highly relevant consideration of the risk to elderly and vulnerable residents from asymptomatic transmission", said the judges.
Despite "growing awareness", the issue was not addressed until the middle of the following month, when testing was made a requirement, they added.
A spokesman for Hancock said in response that the public health body had "failed to tell ministers what they knew about asymptomatic transmission".
"Mr Hancock has frequently stated how he wished this had been brought to his attention earlier," the spokesman added.
- Abandoned -
One of the claimants, Fay Harris, said outside court that Johnson should resign because of the government's "reckless and unlawful" policies.
"Their actions exposed many vulnerable people to a greater risk of death -- and many thousands did die," she told reporters.
"It has only increased the distress to me and many others that the government have not been honest and owned up to their mistakes."
Helen Wildbore, director of the Relatives and Residents Association, a charity for older people needing care, said the ruling confirmed that the government's claim it had thrown up a "protective ring" around care homes was "non-existent".
"Older people were abandoned at the outset of the pandemic," she added.
In parliament, Johnson said the government would study the ruling and respond in due course.
But he added that the early stage of the pandemic was "an incredibly difficult time... and we didn't know very much about the disease.
"The thing that we didn't know in particular was that Covid could be transmitted asymptomatically in the way that it was, and that was something that I wish we had known more about other time," he added.
Britain has had one of the highest death tolls in the pandemic: more than 174,000 people have died within 28 days of a positive test.
In the last seven days, nearly 2,300 people have died, according to the latest government data.