The government’s flagship test-and-trace system will launch at the end of this week, just ahead of Boris Johnson’s June deadline.
Ministers have recruited 25,000 contact tracers as part of what they say will be the largest virtual call centre operation in the country.
But the much lauded NHS app is not expected to be ready in time for the launch.
No 10 said last week that the app, which has been trialled on the Isle of Wight, would be ready within weeks.
Matt Hancock, the health secretary, had set a target of the middle of May to launch the programme, which will trace the contacts of anyone infected with the disease.
People will be warned that they have been in close proximity of someone with coronavirus and be advised to isolate.
Experts say contact tracing is the key to controlling the disease, as seen in other countries like South Korea.
The UK government has faced criticism for abandoning its tracing programme in March when the number of cases became overwhelming.
Mr Johnson has warned that a coronavirus vaccine might still be a year away or, possibly never be found.
Ministers believe the track-and-trace programme is crucial to avoiding a second peak of infections.
Under the system tracers will be in touch with those who test positive for the virus and request the details of anyone they have been in prolonged close contact with recently.
Detailed guidance for the public will be set out later this week.
A No 10 spokesperson said: “A test-and-trace system allows us to isolate new infections so that we can control the spread of this virus, which will be vital while coronavirus remains present in the UK. As we continue on the road to recovery, this will mean that in time lockdown will no longer be necessary for the vast majority of the public and instead it will be possible for there to be a targeted lockdown for a small number of people.
“For this to be effective, everyone will need to stay alert and play their part to control the virus and save lives. By working with our tracers and complying with the rules, the public will avoid unknowingly spreading the virus to their loved ones and this new test and trace service will help to control coronavirus.”