From the NHS website:
The new NHS COVID-19 app, now available to download for free in England and Wales, is the fastest way to see if you're at risk from coronavirus. The faster you know, the quicker you can alert and protect your loved ones and community.
The app has a number of tools to protect you, including contact tracing, local area alerts and venue check-in. It uses proven technology from Apple and Google, designed to protect every user’s privacy. Read more about how we protect your data and privacy.
The free NHS COVID-19 app is a vital part of the NHS Test and Trace service in England, and the NHS Wales Test, Trace, Protect service. Follow these guides for help on how to download and install