World Book Day. Three words that strike panic into the hearts of parents everywhere, who know it means they'll need to whip up a costume for the littl'uns to wear to school/nursery/Scouts/Brownies that day.
Fear not, we've got it covered. These characters are all in books set in London. All of the costumes are relatively easy to throw together (although you can be as creative as you like).
They were all book characters originally, so that'll keep the English teacher happy, although most have since been adapted into films. Yes, we've missed a certain boy wizard and his friends on purpose. Platform 9 3/4 may be in London, but Hogwarts is not.