Question to the Department of Health and Social Care:

To ask the Secretary of State for Health and Social Care, what steps he has taken to ensure that incorrect covid-19 alerts are not sent out from the NHS Test and Trace app.

NHS COVID-19 app users will only be advised to self-isolate if their phone has been in ‘close contact’ with the phone of someone else who has later tested positive for COVID-19.

The app uses Bluetooth Low Energy to understand the distance, over time, between app users. If a user tests positive for COVID-19, the app’s risk-scoring algorithm uses this data, along with the individual’s infectiousness, to make precise calculations about risk to determine whether a user has had a ‘close contact’ and should get an alert. The algorithm has been optimised by scientific experts, based on the functionality provided by V1.6 of Google's and V2.0 of Apple's Application Programming Interface. It is kept under constant review.