> Brexit implied losing Schengen, it was part of it from day 0. Putting back Gibraltar in Schengen.

Gibraltar isn't going into the Schengen, it's just going to follow all of the rules of the Schengen area. It's always(?) required a passport check anyway. It's definitely semantics, though!

> EDIT: not Schengen, sorry, although I'm pretty sure I just used my national (European) ID to go to London many many years ago and not my passport.

You could travel with ID cards pre-brexit. The Schengen area has _no_ checks on the borders, so you don't even need an ID card. (However, the place you're travelling to/from may require you to carry one).