...Personally I just do not understand why Americans have such a problem understanding the many different accents in Britain, I've listened to some pretty impenetrable American accents over the years and never had any problem understanding them, what's the problem?

I always remember back in the early 1970's a programme called 'The Flaxton Boys' which starred the young actor David Bradley who was plucked from obscurity to play the lead role in Ken Loaches film 'Kes' about a young kid from Sheffield in West Yorkshire who tames a Kestrel. His Yorkshire accent in the film Kes was spot on (as you would expect because it was his normal voice) so what did they do? sent him to drama school where they have this idea that to be capable of doing any accent as an actor one must first lose ones natural accent. The result? in the Flaxton Boys, also about boys in West Yorkshire his accent was absolutely fucking awful! I never knew someone who came from Yorkshire could sound so unlike anyone who ever came from Yorkshire? he sounded like he'd never heard a Yorkshire accent in his life!
So much for drama school eh?