A new antibody test that determines whether someone has had coronavirus has shown to be 100% accurate, public health leaders have said.
Boris Johnson has previously called antibody testing a "game-changer" as it may reveal how many people have had COVID-19 without any symptoms and so may be immune.
Any reliable test may help speed up measures to ease the lockdown because people could go back to work confident they were not likely to get it again.
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%.
Health minister Edward Argar said the government wants to roll out the antibody test to frontline workers first.
Speaking to BBC Breakfast, Argar said: "We're in discussion at the moment with Roche on this.
"It's only just gone through the Public Health England assessment as being reliable, as doing the job, and therefore we are having those discussions.
"But we are keen to get as many as quickly as we can and get them out, primarily to the front line first, the NHS, social care and then more widely.
"Because this really will be – as the prime minister said – this has the potential to be a game-changer."
However, Argar added that the government is not yet in a position to roll out the new antibody tests to the public.
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Speaking to BBC Radio 4's Today programme, he said: "It has only just got the green light.
"Obviously we will have had kits to test, but we are not in a position at this point to give these tests out...
"So we're not in a position yet to roll it out to the public and have those tests ready to go."
News of the test was cautiously welcomed by other health workers.
GP and TV doctor Dawn Harper described the results as “exciting” – but said more work was needed in determining whether antibodies meant someone had immunity to COVID-19.
She told Talk Radio: “Potentially it’s a game-changer. We've always said that knowing about herd immunity and who's been infected would help us get out of lockdown in a more structured way.
“This test is potentially really exciting...
“What isn't clear is whether the presence of antibodies equals immunity and how long for and so that is some ongoing work that needs to be done.
“We need to know the presence of those antibodies in the real world means that you are immune to the infection. But it is definitely a very positive step.”
Professor John Newton, national co-ordinator 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.”
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.