A test to find out whether people have ever been infected with coronavirus has been approved by health officials in England.
Public Health England said an antibody test developed by Swiss pharmaceutical company Roche is a “very positive development”.
The blood test looks for antibodies to see if a person has already had the virus, and may now have some immunity.
Until now, officials had said these tests were not sufficiently reliable.
But sources say this is the first one to offer serious potential.
Experts at the government’s Porton Down facility evaluated the test last week, Public Health England said, and found it to be “highly specific”.
Prof John Newton, national coordinator of the UK coronavirus testing programme, said: “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.”
Roche is understood to be in talks with the Department of Health and Social Care about possible use by the NHS in England, though other testing products are also being assessed.
Health officials in Scotland, Wales and Northern Ireland make their own decisions, but are likely to follow suit if England does adopt it.
The device already has approval from medical regulators in the EU and the United States.
But it is not yet clear what amount of immunity from coronavirus a patient might gain from having previously been infected.
An antibody test for coronavirus has long been seen as an important part of the toolkit for plotting a route out of lockdown restrictions.
If workers have already had the virus and gained immunity they are safe to go to work – especially health and social care staff.
Recent attempts to buy antibody tests have floundered because they have been deemed unreliable.
Sources say this latest test device, produced by Roche, is the first to offer serious potential.
Talks are underway with the government over whether it can be produced at scale and at a reasonable cost.
Understandably, Whitehall sources are not giving much away because they don’t want to undermine their negotiating hand.
‘False hope before’
Last week, Health Secretary Matt Hancock said the UK was in talks with Roche about a “very large-scale roll-out” of coronavirus antibody testing.
But he acknowledged there had been “false hope before” and that he would only make an announcement when the government was “absolutely ready”.
The Department of Health and Social Care said an announcement on antibody testing would be made “in due course”.
A spokeswoman said: “Antibody testing is an important part of our strategy to counter the spread of Covid-19 and to help us understand who has had the disease.”
In other developments:
LOCKDOWN HEROES: Stacey Dooley is on the hunt
HOSPITAL SPECIAL: The human stories behind the headlines