The NHS COVID-19 app is entirely voluntary and you can choose whether or not to download it. You can also uninstall and delete the app whenever you like.
The app is not pushed automatically to smartphones. However, if you share an Apple or Google ID, it's possible that the app is installed on your smartphone because a family member has installed it on another smartphone. You can read more information about this:
Read more about the reasons for downloading the NHS COVID-19 app.