The NHS coronavirus app’s advisory board is split over whether it has the authority to tell the government to ditch its version and switch to a decentralised model proposed by Apple and Google. After a meeting on Thursday, it emerged that members argued their role on the board is limited to providing guidance on ethical questions – and not to branch out into a broader discussion of whether the app is the right tool for the job. The UK’s contact-tracing app – which will alert people of the need to self-isolate if they have come into contact with an individual who reported coronavirus symptoms - is controversial because of its centralised design. Other countries’ apps use a decentralised model. Under a centralised system, data is uploaded from phones to a central NHS server for analysis. Under a decentralised system, the data remains on the phones. There is growing acknowledgement within No 10 that the NHSX app is having difficulties and may not survive in its current form following trials on the Isle of Wight. Software for a centralised version by Apple and Google is expected to be released on Tuesday. While there are data ethics questions raised by the government’s app, which will collect data about the spread of the disease and store it centrally for analysis, some of the members’ concerns focus on more prosaic issues, like uptake or effectiveness. As a result, the board has publicly limited itself to expressing concerns about the problems that the current approach could cause, rather than suggesting alternative routes. In a letter to Matt Hancock from 24 April, released on Tuesday, the board’s chair, Jonathan Montgomery, that the app must follow six basic principles, including “minimised” data collection and voluntary use. It came as members told the Guardian of concerns that a lack of transparency and a rush to deploy the technology without proper testing risk compromising the project. Several members said they felt their work had been impeded because they had been given limited oversight. On Thursday the board convened for its regular weekly meeting. The agenda was understood to include the merits of centralised and decentralised models for a tracing app, as well as preliminary results from the Isle of Wight trial. Some members are particularly concerned that they were not informed about the development of a second, parallel NHS app that was being built in secret until its existence was disclosed by the Financial Times last week. The board members, who spoke on condition of anonymity, said they were only shown a draft of a key legal document assessing the app’s potential privacy impacts, and did not see the final version of that document until it was published. They also expressed frustration that a letter sent last month from the board to the health secretary, Matt Hancock, advising on ethical principles that should guide the app’s design, was withheld from the public for several weeks. After repeated complaints from members of the board, the letter was finally published on a government website on Wednesday, alongside the government response. A source on the board said there had been “many failings around communication and transparency” that they believed had inhibited them from being able to properly carry out their oversight role. They said the final version of the data protection impact assessment (DPIA) was “substantially different to the draft we’d been asked to comment on before it went public”. They added that they were “not impressed” by the government’s legal explanation for its data collection. Another member of the oversight board described the DPIA as “disappointing”. Another member warned that the app remained incompatible with some devices. One board member cautioned that while the Isle of Wight trial would provide useful data on how many people would be willing to download it, it would be of limited use in assessing how effective the app would be at tackling the disease, because most residents using it would still be under lockdown. The premise of a contact-tracing app is that phones with the software installed will log their contact with one another using Bluetooth. If a user notifies the system they have Covid-19 symptoms, other users who have been near them will be warned and asked to take appropriate steps. One of the members of the oversight board expressed frustration that the first they knew of government plans to commission a second version of the app, based on the principles of a decentralised model, was when they read about it in the the press. “I think if we are going to fulfil our role in good faith, providing the government with ethical guidelines for its app, then we need to have oversight of the plans,” the board member told the Guardian. “We should not be expected to read about an apparently parallel app being developed in secret until it was reported by the FT. We knew nothing about that.” The Financial Times reported the second app being developed was a back-up, and had been commissioned after pressure within the government over technical and ethical issues with the first app currently being trialled in the Isle of Wight. In their letter to the health secretary last month, the advisory board members warned that the UK’s failure to meaningfully improve its testing infrastructure could prevent the app from operating properly. They also warned against rushing the development of the app. In an email to the Guardian, the board’s chairman, Sir Jonathan Montgomery, said the government had accepted the six principles that the ethics board had suggested should inform the app’s design. “Given the scale of the threat from the pandemic, the NHS needs to act quickly to identify how technology can best be used to protect people,” he wrote. “The board has received early sight of papers and had regular briefings from those involved in building the app. This has enabled us to provide advice which has been positively received.”