An estimated 43,000 people may have been given wrong negative PCR Covid test results, the UK Health Security Agency (UKHSA) has said.

NHS Test and Trace has suspended testing operations provided by Immensa Health Clinic Ltd at its laboratory in Wolverhampton, following an investigation into reports of people receiving negative PCR test results after they have previously tested positive on a lateral flow.

A negative PCR means people will not have needed to isolate and could potentially have spread the infection to many other people.

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.

Dr Jenny Harries, the chief executive of UKHSA, told the BBC it was likely only a few thousand of the 43,000 affected were still infectious.

She added that it was “not clear yet” what went wrong in the private laboratory, adding that it was “accredited to all of the appropriate standards”.

NHS Test and Trace 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.

Dr Will Welfare, public health incident director at UKHSA, said: “We have recently seen a rising number of positive LFD (lateral flow) results subsequently testing negative on PCR.

“As a result of our investigation, we are working with NHS Test and Trace and the company to determine the laboratory technical issues which have led to inaccurate PCR results being issued to people.

“We have immediately suspended testing at this laboratory while we continue the investigation.

“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.

“If you get a positive LFD test, it’s important to make sure that you then get a follow-up PCR test to confirm you have Covid-19.

“If you have symptoms of Covid-19, self-isolate and take a PCR test.”

The Government awarded Immensa a £119 million contract in October 2020 to urgently “develop volume for PCR testing for Covid in line with test and trace requirements”, the contract shows.

The contract did not go to tender under rules allowing urgent responses to the pandemic.

A further £50 million was awarded to Immensa by the Government in a contract last September.

Immensa was incorporated as a company in the UK in May 2020.

According to the Immensa website, the firm was new to Covid testing. It said: “In 2020, we adapted and evolved into Covid-19 testing, taking advantage of our laboratory network, scientific expertise, and digital systems to deliver world-leading Covid-19 testing solutions.”

Andrea Riposati, chief executive of Immensa, said: “We are fully collaborating with UKHSA on this matter.

“Quality is paramount for us. We have proudly analysed more than 2.5 million samples for NHS Test and Trace, working closely with the great teams at the Department for Health and UKHSA.

This will undoubtedly impact people's confidence in the accuracy of these types of tests ... they could have cost lives

“We do not wish this matter or anything else to tarnish the amazing work done by the UK in this pandemic.”

Among the testing sites affected are Newbury Showground in Berkshire.

A man from nearby Swindon said his confidence in the accuracy of his recent Covid test result has been impacted by the issue at the Immensa laboratory.

Tim Barton, 48, told the PA news agency he and his family received positive lateral flow tests after falling ill with coronavirus symptoms earlier this month but their PCR tests came back negative.

The client relationship director said: “My son, daughter and myself all had positive (lateral flow tests) – we then had PCR tests done at the test site in Swindon all of which came back negative.

“This will undoubtedly impact people’s confidence in the accuracy of these types of tests… they could have cost lives.”

Meanwhile, in Wales, about 4,000 people may have been affected from testing sites in the Gwent and Cwm Taf Morgannwg areas.

Dr Kit Yates, a mathematical biologist at the University of Bath, said: “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.

“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.”

Mr Riposati is also chief executive of Dante labs.

The Competition and Markets Authority (CMA) announced in September it was investigating Dante Labs over concerns it may be treating customers unfairly.

This included by not delivering PCR tests and/or results on time or at all, failing to respond to complaints or provide proper customer service, refusing or delaying refunds when requested and using terms and conditions which may unfairly limit consumers’ rights.

The CSA said Dante was “a popular provider of PCR travel tests in the UK this summer”.