At Prime Minister's Questions today, Boris Johnson promised the UK would have in place a "world-beating" system to test and trace people who may have been exposed to coronavirus.
He said 24,000 out of 25,000 contact tracers had already been recruited, referring to teams of people who identify who has been in contact with a person who contracted coronavirus, to notify them so they don't infect others.
But Mr Johnson did not mention the contact-tracing mobile phone app trialled on the Isle of Wight, which uses Bluetooth to detect and record other app users and notifies you if you've been near someone who later develops symptoms.
BBC health correspondent Nick Triggle says that what launches on 1 June will effectively be a prototype track-and-trace system, not a fully functioning one. While contact tracers will be available, the app may not be ready on day one, he adds.