Martin---you're kidding again!?!?
Seriously----I could name a host of artistes in the UK who are bluegrass and country fanatics and wouldn't dream of singing in anything other than an American accent; usually mimicked, I admit.
The worst accent? Well if by that is meant the most unintelligible, Dylan is unbeatable in any part of the world other than North America.
I forgive him, mind you, if I have the lyrics to refer to;he has some top class material.