An NHS app that aims to track the spread of coronavirus is being rolled out for the first time, as part of a trial on the Isle of Wight.
Council and healthcare workers will be the first to try the contact-tracing app, with the rest of the island able to download it from Thursday.
If the trial is successful, it could be available nationwide within weeks.
Concerns have been raised over privacy, though ministers say the app has been designed with this "front of mind".
The app aims to quickly trace recent contacts of anyone who tests positive for the virus.
It is part of the government's strategy for coming out of lockdown, which aims to have widespread testing and contact tracing in place to monitor and reduce any future outbreaks.
If the trial is successful, the app will be rolled out across the whole of the UK by the middle of May, Health Secretary Matt Hancock said.
Meanwhile, Labour leader Sir Keir Starmer has called for a "national consensus" on tackling the virus when the UK begins to move out of lockdown.
It comes as the the number of coronavirus-related deaths in the UK reached 28,734, an increase of 288.
The daily increase in deaths is lower than at any point since the end of March, but the figures reported at the weekend tend to be lower and are expected to rise, Mr Hancock said.
How does the app work?
The new app – published on Apple and Google's app stores – works by using a Bluetooth connection.
It records when two people who have the app are within 2m of each other for more than 15 minutes.
If one of those people later reports having symptoms, all the other app users they came into significant contact with over recent days will be alerted and, if judged necessary, told to self-isolate.
"The exact advice on what you should do will depend on the evolving context and approach," the NHS has said.
Mr Hancock urged everyone on the Isle of Wight to download the app when it was available to them. Social distancing rules would still be in place during the trial, he said.
"By downloading the app, you are protecting your own health, you are protecting the health of your loved ones and the health of your community," he said.
"Where the Isle of Wight goes, Britain follows."
The island was chosen for the trial because it has a lower number of new infections, is covered by a single NHS trust and because travel to and from the island is quite restricted.
Mr Hancock told BBC Breakfast the app would be an "incredibly important part" of the fight against the virus and the more people who downloaded it, the more lockdown restrictions could be eased.
The type of approach used to design the app has raised some privacy concerns.
The app has been designed with a "centralised" approach, meaning there is a central computer which works out which phones have matched and should receive an alert.
This is different to the "decentralised" model used by Apple and Google, where the matches take place on users' handsets.
Some have argued a "centralised" approach gives the app advantages, for example by making it easier to spot hotspots where the disease is spreading. But others say a central system increases the risk from potential hackers.
The UK's data privacy watchdog, the Information Commissioner's Office, said "as a general rule, a decentralised approach" would be more in keeping with its principle that organisations should minimise the amount of personal data they collect.
"But that does not in any way mean that a centralised system can't have the same kind of privacy and security protections," said Information Commissioner Elizabeth Denham on Monday.
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At a virtual meeting on Monday, Parliament's Human Rights Committee also discussed privacy fears. Law professor Orla Lynskey said the option on the app for users to opt in and share their location data "poses a big risk".
But NHSX – the part of the health service that developed the app – said the app will be voluntary, and the only personal data stored by the app at the start would be the first part of the user's postcode.
Additional location data will only be recorded if users agree to a further opt-in request, NHSX added.
Apple and Google have said apps that adopt their decentralised model would not be allowed to gather location data.
NHSX chief executive Matthew Gould said: "The app is designed so you don't have to give it your personal details to use it – it does ask for the first half of your postcode but only that.
"You can use it without giving any other personal details at all – it doesn't know who you are, it doesn't know who you've been near, it doesn't know where you've been."
Mr Hancock said the software was "designed with privacy and security front of mind". He said the data was stored on the phone and only sent to the NHS when someone needs a test.
The UK's "test, track and trace" strategy has seen testing be scaled up over the last month, following Mr Hancock's pledgeRead More – Source