The new NHS Test and Trace app will allow people to delete records of their visits to pubs and restaurants, but will only function on the more modern smartphones.
The app, launched on Thursday, will rely heavily on QR code technology which users will be expected to scan on their way into hospitality and other public venues, creating a digital record of where they have been to be stored on their phone.
However, it has emerged that this will only work on iPhones built in or after 2015, and Android devices with the Marshmallow 6.0 software released in the same year. Charities warned that risks harming older people, who are more likely to use less up-to-date phones and are already more vulnerable to Covid-19.
It came amid reports from Newham, in London, one of the areas where the new app had been tried (it was also trialled at a drive-through testing centre in Catford – see video below), suggesting that just one in five customers to local pubs had scanned the QR code, a camera function that recognises a unique location code that is stored on the user's phone.
The function enables the app to alert people that they should self-isolate if another visitor to that venue tests positive for coronavirus.
Senior officials in NHS Test and Trace have confirmed that, due to privacy concerns, users will be free to delete the record of their movements from the app but will still be alerted if a contact tests positive.
Based on Apple and Google's privacy-centric software, the app marks the second attempt by the Department of Health and Social Care (DHSC) to develop a software to bolster the contact tracing effort. A first version that stored some information centrally was ditched after an unsuccessful trial on the Isle of Wight in May.
The new version has recently been trialled again on the island and in Newham, one of the most ethnically diverse boroughs in the country, as well as among some NHS staff. Officials said the take-up in those areas was between 10 and 30 per cent.
Recent research by Oxford University predicts that contact tracing apps begin to be effective once around 15 per cent of the population download and use them.
But one expert said that, however well the technology works, it is currently "functionally useless" because of the delays in the community testing system.
Professor Lillian Edwards, from Newcastle University, said the goal of effective Covid-19 contact tracing was to isolate close contacts of positive cases before they potentially show symptoms but, with test results in some areas taking seven days to come back, this was impossible.
As well as using QR codes in venues, the app relies on Bluetooth technology to make a record of close contacts – those who have come within two metres for 15 minutes.
Users who have tested positive for coronavirus or who have suspected symptoms are expected to upload those into the app, whereupon close contacts will be told to self-isolate.
The app also has a function that enables users to book a test, as well as a local risk-level alert. It is available to people aged 16 and upwards, and is currently available in eight languages.
Matt Hancock, the Health Secretary (speaking about the UK's surging infection rate in the video below), said: "We have worked extensively with tech companies, international partners, and privacy and medical experts – and learned from the trials – to develop an app that is secure, simple to use and will help keep our country safe.
"The launch marks an important step forward in our fight against this invisible killer, and I urge everyone who can to download and use the app to protect themselves and their loved ones."
NHS Test and Trace said recent updates had "ironed out" glitches with the QR code scanning technology. All public venues are now required to create their own QR code, which they can do via the Government website. Businesses face fines of up to £4,000 if they fail to display the NHS QR code.
Caroline Abrahams, the charity director at Age UK, said: "It's unfortunate that you will need a relatively new smartphone to use the NHS app, since many people of all ages don't have one, older people especially.
"When you add in the very significant numbers of older people who don't own a smartphone at all, the upshot is that the NHS App seems likely to pass much of the older population by."
Helen Milner, the CEO of the Good Things Foundation, a charity that focuses on digital inclusion, warned that the app could widen the digital divide, saying: "If you cannot afford to upgrade your smartphone or you cannot afford the data, you are going to be more at risk of catching and spreading Covid-19."