The NHS is testing its next Covid-19 contact tracking app at a Royal Air Force base in North Yorkshire.
It works by using Bluetooth signals to record when smartphone owners are close to each other, so if someone develops symptoms of Covid-19, an alert can be sent to other users who may have become infected.
In its current state, it tells users: “Are you okay now”, or: “You have to isolate yourself and stay at home”.
The health secretary for England said the trials “are going well”.
“The more people who sign up for this new app when it is active, the better our response will be and the better the protection of the national health service will be,” said Matt Hancock in the House of Commons.
He added that the software would be used in conjunction with medical tests and man’s manual search for contacts.
But some experts argue that the government may place too much trust in technology.
“We don’t need expensive, expensive apps where people will be exposed to data privacy concerns,” Prof. Allyson Pollock, director of the University of Newcastle for regulatory science, told BBC News.
“We should follow … a low-tech model, using people and phone [interviews].
“The clinical observation, which we have found in China, Singapore and Korea, is actually more efficient and offers many more positive aspects.”
The NHS hopes to release the app by mid-May, although the government will make a final decision on the timing.
RAF Leeming was chosen to host the trial version of an early “alpha” version of the software, as it has previous app testing experiences and other new trials on behalf of the military.
He created a scenario designed to simulate the experience of people shopping, using Bluetooth LE (low power consumption) signals to record when two phones were close to each other.
One of these phones would then be used to record the fact that the user had become “infected” in the experiment, causing a cascade of alerts sent to other handsets that had previously been within range.
“We still have to apply the rules [on] social distance as we build it, “said Captain Blythe Crawford.
“So we created a scenario where people will leave their phones on a table simulating that it is located in a shopping arcade, for example, while other people might pass by and look in the shop window and their phone happens to turn up close to a other. “
The on-screen warning for those considered to be at risk says, “If you are on public transportation, go home following the most direct route. [and] stay at least 2m [6.6ft] away from people if you can … find a room where you can close the door [and] avoid touching people, surfaces and objects “.
There are plans for a more realistic follow-up “beta test” later – possibly in a remote community, where its use would be voluntary – within which the text is likely to have been refined.
The tool was developed by the health service digital innovation unit, NHSX.
He said that the alerts will be sent “anonymously”, so users will not be told who triggered an alert.
NHSX has also promised to publish its key designs for security and privacy, as well as the source code of the app, so industry experts can help ensure it is “world class”.
The division is working with Apple and Google on the project but has yet to confirm whether it will adopt their protocols.
The two companies are pushing developers to adopt a “decentralized approach”, so it would be impossible for specific users or those with whom they had come into contact to be identified by the authorities or any other external party.
In any case, NHSX believes that its system already prevents it from being able to identify users until they request a swab test.
NHSX also believes that it has found a way to ensure that its software continues to run in the background on iOS devices.
If true, this would avoid a problem that has limited the adoption of a similar app in Singapore.
Epidemiologists have said that 80% of smartphone owners must use the app to suppress, rather than slow down, the spread of the virus after the blocking measures have been relaxed.
But since around 12% of smartphones in active use in the UK don’t support the required Bluetooth LE standard, the target figure will actually be higher.
And the government is examining ways to increase engagement.
One option under consideration is to provide low-cost wearable Bluetooth devices to those without a compatible receiver.
A similar program is already being tested in Bulgaria to track people quarantined during the coronavirus pandemic.