Senior health officials are facing demands to reveal how much has been spent on millions of inaccurate coronavirus antibody tests, after it emerged that payments had been guaranteed even if the kits failed to work.

Public Health England is also being asked to disclose which companies the tests came from and why payment was not made contingent on the tests proving accurate. A formal request for the details is being made in a letter by Greg Clark, the former Conservative cabinet minister and chair of the Commons science and technology committee.

Britain ordered at least 3.5 million of the antibody home-testing kits, which are designed to detect whether someone has had coronavirus. The UK government talked up the potential of the tests last month, with Boris Johnson heralding them as a “game-changer” that could give individuals a “green light” to go back to work. Health chiefs said kits could be made available through Amazon and Boots once they had been proved to work. However, all the versions of the tests proved to be too inaccurate to be used.

Scientists have discovered that although the tests can show that a person has been infected with a coronavirus, they cannot adequately differentiate between the virus that is causing the current Covid-19 outbreak and other types of coronavirus –which just cause colds. They found that a range of devices all produced far too many false positives.

“It does seem surprising that these tests were bought with a contract that wasn’t contingent on their usability,” Clark told the Observer. “In learning lessons through this crisis, it’s important for future contracts to recognise this risk.”

Kathy Hall, director of Covid-19 testing strategy at the Department for Health and Social Care, revealed last week that the government was working to recoup money paid for the tests “where possible”. Asked whether payment was made on the assumption that the devices worked, she said: “Our overall strategy was to secure tests in order to get them validated. That meant ordering minimum volumes in order to secure them. And we wanted to make sure we had the opportunity to do that, so that was the strategy we took, yes.”

Antibody tests are considered to be vital to moving out of the lockdown caused by Covid-19. They will show whether people have or have not been infected with the the Sars-Cov-2 virus. Health workers found to have antibodies would no longer have to worryabout being infected or infectious every time they display symptoms similar to those of Covid-19, for example.

In addition, antibody tests will give scientists a far clearer picture of how far the Sars-Cov-2 virus has affected the British population, said of Cambridge University’s biostatistics unit. “Knowing how many of us have been exposed to the virus is important for calculating accurately the death rate of this virus among all who were infected. As importantly, the proportion of the population who still have antibodies and – we hope – immunity, has implications for what the future of the epidemic might look like.”

Facebook Twitter Pinterest A deserted street in Gangelt in Germany, where 14% of the population were found to have antibodies for the disease. Photograph: Sascha Steinbach/EPA

The importance of this approach was highlighted last week by a study by the University of Bonn. Researchers there tested a randomised sample of 1,000 residents of Gangelt, a town near the Dutch border that had suffered a major outbreak of Covid-19. They found that 2% of the population was currently infected and 14% were carrying antibodies, which suggested that they had already been infected, although many had displayed no symptoms.

If correct, these figures suggest that if many more people have been infected than was expected, the overall death rate - at least in Germany - from the Sars-Cov-2 virus could be very low. One estimate suggested it would be as low as 0.2%.

These figures have been welcomed, albeit with caution, by scientists in the UK. Professor Keith Neal of Nottingham University, described the study as “good news”, because it suggested that significant numbers of people had developed antibodies and the overall mortality rate could be lower than current estimates.

“The findings are dependent on the quality of the antibody test used, however, and it is important that similar antibody studies are done elsewhere and that results of the antibody tests from Porton Down lab in the UK are reported regularly without delay.”