Anybody know the accent?

It's the accent from the Forest of Dean area, near the Welsh Border. That's where Potter grew up and many of his plays are set there (at least partially).

http://en.wikipedia.org/wiki/Forest_of_dean

As a yank, I found that the subtitles helped a lot in figuring out the accent. Once you get an idea of the idioms actually are ("Thou bist", etc...), you can start figuring out what they're saying.

We don't have to suffer, we're the best batch yet.