An NHS app that alerts users to recent contacts who are infected with coronavirus will be ready for deployment within three weeks, according to the chief executive of NHSX, the digital arm of the health service. Matthew Gould told MPs on the Commons science and technology committee on Tuesday that the contact-tracing app would be trialled in a “small area” and available for use next month provided it performed well. But while the app will be ready in two to three weeks, its widespread rollout will depend on the strategy ministers adopt around easing the lockdown and the availability of testing, which is crucial for the app’s success. Ministers are working through proposals on how to refine the lockdown over the coming weeks without allowing the reproduction rate of the virus to rise above one, the point at which infections would rise again. “We are, I hope, on course to have the app ready for when it will be needed, at the moment when the country looks for the tools to come out of lockdown safely,” Gould told MPs. The NHS app uses short-range bluetooth signals to record when people are in close proximity for a specified period of time. It then issues automated alerts to those at risk whenever a fellow user records a positive test for the virus. The alerts will not disclose who has triggered the warning, but will advise contacts to seek a test or self-isolate. The app’s developers have built the system around a “centralised” platform following discussions with advisers including GCHQ’s National Cyber Security Centre. In the centralised model, contacts are represented by an “identifier” and matched on a central computer. The approach contrasts with that being taken by Google and Apple for a similar contact-tracing app where matches are performed on users’ mobile phones. The tech firms claim their approach is more secure because there is no central server that governments or hackers can access to track people and those they meet. Prof Lilian Edwards, an expert in internet law at Newcastle University, told MPs that the centralised approach raised questions about privacy. “There’s an intrinsic risk in building any kind of centralised index of the movement of the entire population which might be retained in some form beyond the pandemic,” she said. “We have a precedent of other pandemics leading to a mass land grab in extensive state surveillance, that is my worry.” She added, however, that the “devil is in the detail”. Gould said there were “a series of protections” that meant people should be confident that their privacy would be respected when using the app and that the data would only be used to control the outbreak and for NHS care and research. He warned that without a public awareness campaign, it would be “tough” to get enough people, estimated at 80% of smartphone users, to use the app. “The message needs to be: ‘If you want to keep your family and yourselves safe, if you want to protect the NHS and stop it being overwhelmed and at the same time we want get the country back and get the economy moving, the app is going to be an essential part of the strategy for doing that,’” he said. But Prof Christophe Fraser, a senior group leader in pathogen dynamics at the University of Oxford’s Big Data Institute, told the committee that if roughly 60% of the population used the app, that would be enough to keep the reproduction number or the virus below one, meaning the epidemic could be contained.