Originally Posted by Digital Sid:
“Not a wholly authentic one, but near enough.”
My understanding is that his public accent is his own natural accent, the product of growing up in the United States, and that his Scottish accent is something that kicks in around his parents.
There are as many regional accents in the United States as there are in the UK. I've noticed that Brits tend to be far more critical of British actors' American accents than Americans are. I've heard accents savaged here where I had no inkling the actor wasn't American. (Granted, I'm not American, but I certainly have a lot more exposure to American accents than British people do).
On the other hand, Dexter Fletcher's supposedly "so good fans thought he was American" accent in Press Gang and (in one episode) Hotel Babylon was absolutely appalling.