A new test to determine whether people have ever been infected with coronavirus is 100% accurate, public health leaders have said.

Prime Minister Boris Johnson has previously called antibody testing a “game-changer” as it may reveal how many people have had Covid-19 and may now have a degree of immunity.

Public Health England (PHE) said last week scientific experts at its Porton Down facility had carried out an independent evaluation of a new antibody blood test developed by a Swiss pharmaceutical company.

The examination found Roche’s serology test was “highly specific” and had an accuracy of 100% in detecting people who had ever had Covid-19.

Professor John Newton, national coordinator of the UK Coronavirus Testing Programme, said although it was still unclear to what extent the presence of antibodies indicated immunity to Covid-19, it was a “very positive development”.

He added: “We were confident that good quality antibody tests would become available when they were needed.

“Last week, scientific experts at PHE Porton Down carried out an independent evaluation of the new Roche Sars-CoV-2 serology assay in record time, concluding that it is a highly specific assay with specificity of 100%.

“This is a very positive development because such a highly specific antibody test is a very reliable marker of past infection.

“This in turn may indicate some immunity to future infection although the extent to which the presence of antibodies indicates immunity remains unclear.”

News of the test comes as:

– Mr Johnson announced a £600 million package for coronavirus infection control in English care homes.

– The Prime Minister said he owed “everything” to the NHS, writing in the Sun: “They have risked lives for us. And tragically, have given us – a debt we can never begin to fully repay”.

– Police have been told they have no powers to enforce two-metre social distancing in England in fresh guidelines issued by the College of Policing and the National Police Chiefs’ Council.

– A 14-year-old boy with no underlying health conditions has died from a Kawasaki-like disease linked to coronavirus.

The antibody test is designed to help determine if a patient has been exposed to the virus that causes Covid-19 and whether they have developed antibodies against it.

The detection of these antibodies could help to indicate if a person has gained immunity against the virus.

We are exploring the use of antibody testing across the NHS and ultimately the wider public

Mr Johnson said in March that such a test would be a “game-changer”.

A Department of Health and Social Care spokeswoman said: “We are exploring the use of antibody testing across the NHS and ultimately the wider public.

“We are delighted that devices are progressing through validation, and are actively working on our plans for rolling out antibody testing and will make announcements in due course.”

Health Secretary Matt Hancock last week said the UK was in talks with Roche about a “very large-scale roll-out” of coronavirus antibody testing.

The findings come as Dr Mike Ryan, executive director of the WHO’s health emergencies programme, told the FT’s Global Boardroom digital conference no-one could predict when the disease would disappear.

He said: “We have a new virus entering the human population for the first time, and therefore it is very hard to predict when we will prevail over it.

“And it is important to put this on the table – this virus may become just another endemic virus in our communities. And this virus may never go away.

“HIV has not gone away, we’ve come to terms with the virus and we have found the therapies and we found the prevention methods, and people don’t feel as scared as they did before and we’re offering long healthy life to people with HIV.”

Mr Johnson will chair Cabinet on Thursday, the day after grim economic figures were released and some lockdown restrictions in England were relaxed.

After the data showed the economy shrank by 5.8% in March, Bank of England governor Andrew Bailey warned Britain was in a sharp slide to recession.

He told ITV’s Peston: “Well, I think it tends to confirm that we’ve got a very sharp move into recession and it was quite sudden, which is obviously what we’ve all observed from the shutting down of the economy so, to be frank, we’re not really surprised by that number at all.”