Are the actors and actresses speaking essentially in the accents with which they were raised? Is there anyone who’s doing something notably different? How, from a class or regional perspective, would you describe the accents of Harry, Ron and Hermione? Are the Weasley family members’ accents consistent with each other?
Mods, if this should be in CS or even GD, feel free to move it.
I’ve only ever heard brief parts of interviews with Emma Watson, but from what I can tell, her normal speaking voice does not have the same accent as Hermione’s.
As far as I can tell Daniel Radcliffe and Emma Watson hardly change their accents for Harry and Hermione - fairly standard southern English. Emma Watson in real life is a bit posher, more “public school” but not much. Ron is still southern English but maybe more lower middle class. To somebody (like me!) living in Oxfordshire both the actors and the charecters sound “normal” - they don’t stand out from the voices I hear every day.
I heard that for the Philosophers Stone Emma had a speech coach, because she was not using her normal accent.
The main trio and Draco Malfoy are all from middle-class South-East English families; Ron’s accent might be a little more working class than Rupert Grint’s, but it’s probably natural or close enough.
Alan Rickman’s background’s London working class, so his childhood accent was probably not posh like it is now.
Maggie Smith’s usual accent is RP, though it might have been more estuary when she was a kid, and it certainly wasn’t Scottish (although her mother was Scottish).
Michael Gambon’s accent was probably working class London as a kid, then stage school posh, and he would only have had the accent he uses in the films when he was a very small child in Dublin.
Robbie Coltrane is Scots, definitely not Forest of Dean like Hagrid.
The Weasley family have vastly different accents:
The Dad’s accent is West Midlands - not sure what the actor’s original accent is like, but Worcestershire accents can sometimes be a bit midlands.
The Mum seems to be speaking with a soft Manchester accent or something similar; Julie Walters is from the Midlands but has used lots of different accents in her career.
The twins are both from a town near Birmingham and sound like it.
Ginny has a generic Southern accent which is also probably her natural accent, since she’s from London.
Percy sounds quite posh; I haven’t heard him speak in anything else, but that might be his natural accent, or he might sound like a regular kid from Norfolk.
I can’t remember Charlie’s accent in his brief appearance. Maybe he was Scouse and Bill will be Geordie. 
I assume the Weasleys have moved around a fair bit over the years!
Missed this bit: the notably different ones are Hagrid, McGonaggall and Dumbledore (when played by Gambon), though the latter two do have family connections to the accents of their characters.
Many thanks! Just what I wanted to know.
How does Harry’s accent compare to the Dursleys’ accents?