Why is Les Miserables sung with British accents?

Haha nice question. It sounds weird, but actually all singers with good teachers are *taught* to sing that way. That way, you don't sing with an obnoxious childish or country accent, because accents are always exaggerated when singing. Even if you don't think you sing that way, unless you sing with a bit of a British accent, your vowels tend to sound bad and/or cause you to go sharp or flat, ruining the piece.

When I was in choir, the teachers called it "tall vowels," but they said it like: Towl vahwels. Make your mouth tall and in an O shape: that's what they had us do. :) No lie.