Did I understand correctly that outlets contain a switch and are off by default and that the grounding pin switches them on when inserting the plug? That's great.
Which means you can use a European plug in a UK socket, if you first put something in the earth slot (a key works well).
European travellers are generally impressed when I show them this trick, and sometimes rightly concerned that I'm sticking metal objects into a power outlet. If there's any chance the outlet is wired incorrectly, don't do this unless you can isolate the outlet or the key.
Yeah I wouldn't rely on things being wired correctly. When I moved into my current UK house the neutral and earth were physically connected (someone had driven a nail through a cable and "got lucky"). Took a while to find the nail and fix that.