All modern wiring in the UK has every socket in the building connected via RCD (the more common name for GFCI outside America), but they're usually in the main fusebox/consumer unit rather than individually per socket. These are just normal on/off switches for the convenience of being able to turn things on and off.
That's what I thought at first, but it's literally every socket in this building both inside the apartment and outside in the hallways, and I keep seeing it in other buildings too.
I am doing that, but I'm sort of putting them in appropriate threads. Otherwise I'd be writing a novel. Or I suppose creating a Flying Squid in Britain community. Maybe if I get less exhausted at some point I'll post something long.