Concerns have been raised about the Government's Covid-19 contact-tracing app's reliance on self-reporting and the risk it could be used to "prank" people.
The smartphone download known as NHSX is being trialled on the Isle of Wight before its anticipated roll-out across the rest of the country.
Dr Michael Veale, a lecturer in digital rights and regulation at University College London, said the app's reliance on people self-reporting is "a worry", as well as its inability to work well across borders, such as in Ireland.
He said the United Kingdom is effectively the only country to use self-reporting rather than verified tests in its app. Dr Veale, who is part of a team working on a rival app, told Sky's Sophy Ridge On Sunday: "That appears to stem from not a lack of number of tests potentially, but really something that hasn't been focused on enough - the tests aren't fast enough in the UK compared to other countries.
"And so the UK seems to claim it's stuck using self-reporting because it can't get a test turned around within a few hours.
"And this is really a worry. In other countries we're working with, they are very clear that self-reporting will not be allowed on their app because it can be misused or used to prank or used to target people deliberately and put them into quarantine without them knowing."
Dr Veale said it is "unclear" if the Isle of Wight is a good testing environment for the app.
He added: "One of the challenges is the app needs to be tested in realistic situations, busy situations. And if the Isle of Wight is in lockdown as it is, it's unclear that that is a good testing environment to see if the app really works and particularly around issues like battery when there are a lot of people around."
Meanwhile, a diagnostic expert asked to consult on the Government's app has criticised it for focusing on coughs and fever at the exclusion of other symptoms.
Nick Summerton, a GP with 32 years' experience, told the Sunday Mirror the app risked ignoring 10 symptoms other than fever or cough.