I watch a lot of James Bond movies so I'm used to hearing the very prim and proper British (London?) accent... therefore the "street kids" in "Attack the Block," between the accents and the slang they used, sounded like they came from an entirely different planet
Reminds me of years ago when I met John Gallagher of Raven - hell of a nice guy but his extremely thick Newcastle accent was a little hard to follow.
The receptionist at my job at the time was originally from London and she had the very prim-and-proper Brit accent, I mentioned to her that I'd just met this guy from Newcastle and couldn't help but notice how different his accent was from hers, and she sez "Oh yes, Newcastle accents even sound strange to ME."
Those northerners...
They sound much different than Londoners. Especially South London. Throw in a few scousers for a laugh.
My Grandad was from Newcastle ... when he met someone for the first time, he'd generally revert to a strong Newcastle accent just to confuse/annoy/upset them ... my Mum is Welsh and apparently still has an accent (although, obviously, I don't hear it) ... the 'London' accent has spread East ... Basildon is full of 'Londoners', innit?