I wouldn't count on getting any answers to this thread...there are only a hand full of girls here and I'm relatively certain they don't wear to school.
Never, that's way too much of a risk! I've worn them damn near everywhere else though. Even to random places like Disneyland and stuff...which I suppose you don't have in the UK anyway.
Compression shorts and jeans. The bulk isn't such a big deal unless you're wearing Abenas or something. Regular diapers aren't big enough to make it obvious. There's hardly any noise when you're in public. You'll be the only one who notices.