Speaking during today’s daily Downing Street press briefing, Health Secretary Matt Hancock said the government’s antibody surveillance study has shown that 17% of people in London and around 5% or more of the population in the rest of the country have tested positive for antibodies.

Antibody tests tell a person if they have had the virus and have subsequently developed antibodies in response, that might help them to fight Covid-19 in the future. Mr Hancock said the government has signed contracts to supply 10 million antibody tests, with health and care staff, patients and residents prioritised to receive them from next week.

He added that certification systems will be developed for people who test positive for antibodies, so they can be advised on what they can safely do. While it remains unclear what level of immunity people develop once they have had Covid-19, experts hope a degree of immunity lasts for at least a year or two.

Speaking of the antibody surveillance study, Mr Hancock said: ‘This was based on a sample but for the public at large to know whether or not they have had coronavirus, we need antibody tests are larger scale.

‘Two lab based products produced by Roche Diagnostics and Abbott Labs have been given a positive evaluation by PHE and approved by the MHRA. And three further tests are being assessed right now.’

He added: ‘The UK government has arranged supplies of these tests on behalf of the devolved administrations and each devolved nation is deciding how to use its test allocation and how testing will be prioritised and managed locally.

‘This is an important milestone and it represents further progress in our national testing programme.

‘It’s not just about the clinical advances that these tests can bring although obviously that’s important. It’s that knowing that you have these antibodies will help us to understand more in the future, if you are at lower risk of catching coronavirus, of dying from coronavirus, and of transmitting coronavirus.’

However, independent evaluations of the government’s new antibody tests have discovered they had ‘notable limitations’, experts have warned.

PHE said an antibody test, developed by Swiss pharmaceutical giant Roche, was a ‘very positive development’ after experts at its Porton Down facility gave it the green light.

The test – which Prime Minister Boris Johnson has previously called a ‘game-changer’ – picks up 100% of cases where somebody has had coronavirus in the past, it added.

But Professor Sheila Bird, member of the Royal Statistical Society’s Covid-19 Taskforce, said the evaluations of the Roche test and another antibody test, from US-based Abbott Laboratories, had numerous weaknesses.

She said on Thursday that the evaluations did not take into account the age or gender of the samples, despite men and older people appearing more likely to be more severely affected by the virus.

Prof Bird said that because of this, the tests’ suitability for population surveillance had not been addressed.

Jon Deeks, Professor of Biostatistics and head of the Test Evaluation Research Group, University of Birmingham, also raised concerns over the evaluations.

These included the fact that they are based on samples not patient numbers, the origin and severity of the disease is not known and non-Covid-19 patients with similar respiratory illnesses were not included, he added.

Prof Deeks said the tests ‘fell short of being game-changers’ because while they very rarely wrongly state a non-Covid-19 sample as showing antibodies, they sometimes miss detecting the virus in samples from infected patients.

But a PHE spokesman said it was confident that the volume of samples and methodology was of a ‘high standard’.

He added: ‘These are new tests in a rapidly evolving field of work. Our evaluations have been completed in record time using the samples and tests that were available to us.

‘This is very new territory and stratified age and gender samples are not yet available for Covid-19.’

It comes after Superdrug started selling antibody tests for £69 but some experts have questioned their efficacy. Users will need to take a finger prick blood sample at home and then send it off to a lab.

Results are posted through Superdrug’s Online Doctor portal 24 hours after reaching the lab. If positive, it means the person had the virus at some point.