I can tell you that it's even better for someone who has been to that area of England. Absolutely priceless.
Because of the ambiance or are there jokes in the movie that you only get if you have been there? Grrr, Imrahil
I think it's because it heightens the parody of what the people are like down there. You TOTALLY have people that you cannot understand ONE bit, but the it is clear as day to the people there. Everything is super-chillaxed. Everything's good. So then it heightens the effect of a London Policeman with his hectic energy level arriving there.
I loved this one as a kid, had no recollection of Mark Hamill being in it! I may watch it again purely for kicks.