Far less regulated and accountable than government.
Until that changes. Once people have surrendered a right- such as the right not to effectively wear an electronic tag as a law-abiding citizen- it can be pretty difficult to get that right back. So, once coronavirus is no longer a crisis, maybe, because we all have the app and it could be so very useful in investigating crime and terrorism, maybe we just encourage people to keep it installed, carry on using it. Maybe we offer incentives to do so. Maybe then, as it's so useful and lots of people use it anyway, we pass a law to make it be incorporated as a background app that runs in all new phones sold in the UK. And we sleep-walk into the situation that, if you're involved in any protests or anti-government action, the government know exactly who you are and who you were with.
It's a slippery slope argument, is all.