Testing operations provided by Immensa Health Clinic at its laboratory in Wolverhampton have been suspended, following an investigation into reports of people receiving negative PCR test results after they have previously tested positive on a lateral flow.
The errors relate to test results given to people between September 8 and October 12, mainly in the South West of England, but with some cases in the South East and Wales.
There are no technical issues with test kits themselves and people should continue to test as normal, UKHSA said.
It said a full investigation is being carried out into why and how incorrect results were given.
The government’s NHS Test and Trace service estimates that around 400,000 samples have been processed through the lab, but new samples are now being redirected to other labs.
Test and Trace is contacting people who could still be infectious to advise them to take another test, while close contacts who are symptomatic will also be advised to take a test, as is already recommended.
PCR tests can detect COVID-19 several weeks after infection.
If a person has a positive lateral flow result, they are told to have a follow-up PCR to confirm the finding.