A coronavirus app that alerts people if they have recently been in contact with someone testing positive for the virus "could play a critical role" in limiting lockdowns, scientists advising the government have said.
The location-tracking tech would enable a week's worth of manual detective work to be done in an instant, they say.
But the academics say no-one should be forced to enrol - at least initially.
UK health chiefs have confirmed they are exploring the idea.
"NHSX is looking at whether app-based solutions might be helpful in tracking and managing coronavirus, and we have assembled expertise from inside and outside the organisation to do this as rapidly as possible," said the tech-focused division's chief Matthew Gould.
Instant alerts
The study by the team at the University of Oxford's Big Data Institute and Nuffield Department of Medicine was published in the journal Science.
It proposes that an app would record people's GPS location data as they move about their daily lives. This would be supplemented by users scanning QR (quick response) codes posted to public amenities in places where a GPS signal is inadequate, as well as Bluetooth signals.
If a person starts feeling ill, it is suggested they use the app to request a home test. And if it comes back positive for Covid-19, then an instant signal would be sent to everyone they had been in close contact with over recent days.
Those people would be advised to self-isolate for a fortnight, but would not be told who had triggered the warning.
In addition, the test subject's workplace and their transport providers could be told to carry out a decontamination clean-up.
"The constrictions that we're currently under place [many people] under severe strain," said the paper's co-lead Prof Christophe Fraser.
"Therefore if you have the ability with a bit more information and the use of an app to relax a lockdown, that could provide very substantial and direct benefits.
"Also I think a substantial number of lives can be saved."
To encourage take-up, it is suggested the app also acts as a hub for coronavirus-related health services and serves as a means to request food and medicine deliveries.
The academics note that similar smartphone software has already been deployed in China. It was also voluntary there, but users were allowed to go into public spaces or on public transport only if they had installed it.
One of the ethics specialists involved in the Oxford study said he did not think similar arrangements would be appropriate in the UK, but added that private enterprises might still impose restrictions.
"My favourite restaurant might ask me to show that I was low-risk before allowing me into a crowded place, and I think that would be a perfectly reasonable price to pay for this step towards returning to normal life," Prof Michael Parker told the BBC.
He added that employers might also be justified in requiring staff to use the app if they worked "in an old people's home, with vulnerable groups or [were based] in very crowded places".
And while he said that the general public should not be compelled to use the app to begin with, he did not rule this out if the majority failed to do so.
"The key question is - does it require everyone to do it for it to be effective?" Prof Parker explained.
"It's not essential that everyone does... but perhaps a high proportion of the population needs to.
"This is a really unusual situation where lives are at risk, so there is a case to be made to make at least some actions compulsory - but there would need to be a really clear case for that and careful oversight."
Extended range
The paper adds that the app could be updated to tackle the pandemic more aggressively if required.
For example, it says, the stay-at-home alerts could be expanded to second or even third-degree contacts.
And while the paper advocates the app being used in conjunction with home tests, Prof Fraser said his team was currently exploring whether it would still be effective if it relied on people using a questionnaire or 111 helpline advisers to diagnose the condition.
He acknowledged some people might be wary of using the service, but hoped they would do so to "save a lot of lives".
"We already have tracking apps on our phones for more trivial tasks - the reason we have live traffic information is because we allow the people that provide the mapping service to track us," he said.
"What we're suggesting here is essentially sharing anonymised information [to] put to good use."
