More than 1.7 million people have been asked to isolate since it launched in September.
The NHS Covid-19 app is designed to keep an anonymous log of individuals that people come into close contact with using Bluetooth, as well as allowing users to check into venues by scanning a QR code when restaurants and other indoor public spaces are open.
England and Wales’s app has now been downloaded 21.63 million times, which the Government says equates to 56% of the population.
Scotland and Northern Ireland have their own apps, though the same underlying technology means isolation alerts can be shared between different apps.
But the technology is automated and does not share details of those told to isolate with Test and Trace, as such the number of people who actually obey warnings from the app is unknown.
Research by Oxford University and The Alan Turing Institute – which is still subject to peer review – suggests that the NHS Covid-19 app has so far prevented 600,000 cases.
“The impact of the app could be increased by more people using it: for each increase in users of 1% of the population, the number of cases can be driven down by approximately 2.3%,” said Professor Christophe Fraser at the University of Oxford.
“The epidemiological outlook remains concerning, and using the app can contribute to reducing infections until we are all vaccinated.”
People can book a test via the app and receive the result within it, or can enter the result manually if booked elsewhere.
Between the two, over 3.1 million test results have gone through the app, 825,388 of which came back positive.
Meanwhile, a total of 253 venues were identified as “at risk” due to outbreaks since December 10, triggering “warn and inform” alerts being pinged to users who had checked into those places using posters with a QR code.
The Government said the venue check-in feature has been used some 103 million times.
Health Secretary Matt Hancock said: “The NHS Covid-19 app is an important tool in our pandemic response.
“We know it has instructed hundreds of thousands of at-risk people to self-isolate since it launched in September – including me – and this analysis shows it has been hugely effective at breaking chains of transmission, preventing an estimated 600,000 cases.
“Isolating and knowing when you have been at risk of catching coronavirus is essential to stopping the spread of this virus, and the app is the quickest way to notify you if you are at risk.
“I want to thank all those who have played their part by downloading and using the app, and urge those who haven’t to take the simple step to protect your communities and loved ones and download it.”