A coronavirus test that reveals who has had Covid-19 but not shown symptoms has been hailed as a "game-changer".
The Government's chief scientific adviser Sir Patrick Vallance said Public Health England's (PHE) work on the antibody test is "progressing very fast", and will provide valuable insight into the pandemic.
Speaking at the daily Downing Street press conference, Prime Minister Boris Johnson said development of the test was not far away.
Mr Johnson said: "The great thing about having a test to see whether you've had it enough, is suddenly a green light goes on above your head and you can go back to work safe and confident in the knowledge that you are most unlikely to get it again.
"So for an economic point of view, from a social point of view, it really could be a game-changer.
"You can really see the potential of that advance, which, as I say, is coming down the track."
Sir Patrick added: "That's progressing very fast, Public Health England are looking at this today.
"They've got a test in house they've got going and we're looking at ways at getting the much more widespread version out.
"It is a game-changer. And the reason it's a game-changer is that it allows you to understand the proportion of the asymptomatic population – who's had this disease, but hasn't had symptoms.
"Going forward it's going to be critically important to be able to monitor this disease well because only by being able to monitor it can we start relaxing measures again."
Earlier on Wednesday, the Government announced that it would be ramping up its testing efforts, carrying out 25,000 coronavirus tests per day.
New #COVID19 guidance:
▪️ If someone in your household has a new, continuous cough and/or high temperature, everyone in the household should stay at home for 14 days.
Read the full guidance here: https://t.co/8i4f9JrdtKpic.twitter.com/srho0KOz0p
— Public Health England (@PHE_uk) March 17, 2020
Speaking at the press conference, Dr Jenny Harries, deputy chief medical officer for England, said officials were also looking at Covid-19 tests that could be taken at home.
She explained: "As we go forward, we have an ambition to have some sort of home-based test for the very reason which has been described here – which is we don't want potentially infectious people arriving in hospitals.
"But we recognise that the public, and particularly our key workers, want to understand their status so that they can get back to normal activities."
She added that a lot of work was ongoing in that regard and that "huge" progress had been made in the last few weeks.