The private laboratory that is under investigation for potentially issuing more than 40,000 false negative Covid tests was not fully accredited to perform the work, contrary to assurances made by health officials.

The UK’s independent accreditation service, Ukas, told the Guardian on Monday that neither Immensa Health Clinics Ltd nor its sister company, Dante Labs, had ever been accredited by the service, and that it had informed the Department of Health that statements suggesting otherwise were incorrect.

The UK Health Security Agency announced on Friday that it was suspending operations at Immensa’s laboratory in Wolverhampton pending an investigation into concerns that at least 43,000 people with coronavirus had been wrongly told their swabs tested negative for the virus.

Because many of the individuals would have believed the typically more accurate PCR tests performed by Immensa over simpler lateral flow tests, there is a substantial risk they unwittingly spread the virus on to thousands more people.

Announcing the investigation into Immensa on Friday, Dr Jenny Harries, the chief executive of the UK Health Security Agency, said the lab was “accredited to all of the appropriate standards”, while on Monday a government spokesperson said: “The lab was fully accredited by the UK’s independent accreditation service before being appointed.”

But Ukas said neither Immensa Health Clinics nor Dante Labs had ever been awarded Ukas accreditation, which is intended to ensure labs meet minimum quality standards. Companies require the certification, or must be in the process of applying for it, if they wish to provide Covid testing.

Since November 2020, Ukas has been working with the Department of Health to develop a three-stage accreditation process for private providers of coronavirus testing. Companies that take swabs, test them, or do both, are required to demonstrate that they meet minimum standards by progressing from application to appraisal and final accreditation.

Only after completing the third stage is an organisation accredited by Ukas to perform Covid testing work. So far, Ukas has received more than 500 applications from private firms to perform tests and/or swab handling. About 400 have passed stage two, 255 have had a final stage-three assessment, and 191 have received full Ukas accreditation. An additional 54 public labs, including Lighthouse laboratories, are also accredited.

Ukas does not release information about individual companies and whether they are in the process of applying for accreditation, but in a statement a spokesperson said: “Neither Immensa Health Clinic Ltd nor its related company Dante Labs Ltd has been accredited by Ukas.” Companies are allowed to “self-declare” that they meet minimum standards, but this typically marks the start of an application for accreditation.

Alan McNally, a professor in microbial evolutionary genomics at the University of Birmingham, who helped set up the Lighthouse lab at Milton Keynes, said: “The UK Health Security Agency and Department of Health and Social Care need to make it very clear what they mean by the Immensa lab being ‘fully accredited’. If it is not at all Ukas accredited, and it is not an official part of the Lighthouse lab network, which has its own very rigorous accrediting and validation process, then how exactly was it determined to be fit and proper to deliver Covid testing to the UK public?”

McNally said if the UKHSA investigation into Immensa found evidence of poor management, corner cutting to increase margins, or insufficient staff training “they should be charged and have all contracts terminated”.

Immensa Health Clinics Ltd was set up in May 2020 and received nearly £170m in NHS test-and-trace contracts. The company has been contacted for comment. Earlier this year, the Sun on Sunday found evidence for Immensa workers brawling, sleeping, playing football and drinking on duty while working at the firm’s Wolverhampton lab. The government said at the time it took “evidence of misconduct extremely seriously”.