Slag 101.

I think most people of whatever "Class" in the UK, will all have a vague(if pushed) knowledge of the levels of formality, although I think many would struggle on the finer points. They may not ever wish, or care, to get involved in the social scene, or the opportunity may not ever arise for them even to have the chance and that is a fact, but one Brit's idea of "formal" would be pretty much the same as another's.