A COVID-19 testing laboratory in central England has been suspended over concern that it has been incorrectly giving negative Polymerase chain reaction (PCR) test results to people who are infected, the U.K. Health Security Agency (UKSHA) said on Friday.

Britain's NHS Test and Trace launched an investigation into a lab in Wolverhampton after reports of people getting negative PCR test results after testing positive on rapid lateral flow devices (LFDs).

Government advice says PCR tests are more accurate than LFDs, and people can stop self-isolating if a positive LFD result is followed by a negative PCR test result. UKSHA said that an estimated 43,000 people may have been given incorrect negative PCR test results, mainly in southwest England, possibly underestimating the number of people with the coronavirus between Sept 8. and Oct. 12.

"We have immediately suspended testing at this laboratory while we continue the investigation," said Dr. Will Welfare, public health incident director at UKSHA. "There is no evidence of any faults with LFD or PCR test kits themselves and the public should remain confident in using them and in other laboratory services currently provided."

Immensa Health Clinic, who runs the lab, said it was "fully collaborating" with UKSHA in the investigation. UKSHA said it was an isolated incident in one laboratory, with samples now being redirected to other labs, and overall testing availability was unaffected. But some scientists raised the alarm that the false negatives could have contributed to the spread of infections, which are now at their highest level since July.

"We now know 43,000 people are believed to have been given false negatives, but this doesn’t even come near to the cost of the mistake," Kit Yates of the University of Bath’s Department of Mathematical Sciences said. "Many of these people will have been forced into school or work potentially infecting others. This could be part of the reason behind some of the recent rises we’ve seen."