England's government agency responsible for responding to public health emergencies said mistakes at a testing laboratory resulted in tens of thousands of positive COVID-19 cases reported as negative may have led to the deaths of 20 people.
Britain has one of the highest coronavirus death tolls in the world, with more than 177,000 deaths since the pandemic started in 2020.
An investigation by the UK's Health Security Agency found the Immensa laboratory in central England, was found to have misreported around 39,000 tests as negative when they should have been positive between Sept 2 and Oct 12 last year.
"Through this investigation we have looked carefully at the arrangements in place for overseeing contracts of private labs providing surge testing during this time," said Richard Gleave, UKHSA director and lead investigator.
"It is our view that there was no single action that NHS Test and Trace could have taken differently to prevent this error arising in the private laboratory. However, our report sets out clear recommendations to both reduce the risk of incidents like this happening again."