Your initial claim is that it is not an invasion of privacy, but your argument is only that it is legal. And is it also not an invasion of privacy in China, where facial recognition cameras log everywhere you go in public? Any protest you attend, or coffee shop where troublemakers congregate that you visit, all of it is logged, and you don't even need to carry your phone with you. The UK is showing every intention of reaching parity with China in this regard.

But that's no different than a random photographer taking your picture, or a grandmother noticing you come and go through a window?

I agree "privacy" isn't the perfect word, but seems to be the best one we have to describe what we're losing as surveillance expands.