Concerns were raised at the All Party Parliamentary Group (APPG) on Data about the effectiveness of the NHS Covid App with experts warning that the system will not work.

The meeting heard from Ross Anderson, Professor of Security Engineering at the Department of Computer Science and Technology, University of Cambridge who flagged up problems with a similar system in Singapore.

The app uses Bluetooth which was not designed to measure distance. Your mobile phone can detect that it is within range of another phone. But the strength of a signal does not equate accurately to distance so cannot measure if you have been within two metres of an infected person. Many factors make a difference to signal strength: for example if your phone is in your pocket, in a handbag or sitting on the table next to you; or reflection off a metal surface.

This means Health Ministers are unable to specify what the distance from another app user will be to trigger the app to report a potential covid-19 interaction. In answer to a question posed by Daniel Zeichner MP, the minister would only say that a “sophisticated ‘contact risk model’” will be used.

Daniel Zeichner MP, who chairs the APPG, said: “One metre, two metres, ten metres? The truth is it is impossible to know. Are we going to end up with huge numbers of false negatives or miss other people? At this moment of national crisis it is right that we use every means at our disposal to protect lives but I have many concerns about the app. What is really needed is effective local public health systems to do tracing.”