From Shirebrook?!!?

Bit late to this but yes I agree it might be more near london. Derbyshire not far south of Yorkshire but hardly 'ey up lad call thambulance'. His movements while growing up are not detailed but I am sure he has spent enough time in and around London to slip into that accent. Also as he does not actually SPEAK clearly it is muffled no mater what it is. I certainly do not see him in a WW2 movie as an officer on board a ship or flying a bomber or commanding ground troops. Who would hear him? but good for night ops. I have heard other english actors speaking with RP accents but from further afield. Aussies can sometimes confuse us in disguising that accent becoming almost home counties sounding. Sean Bean does not do it well but no one cares about his accent. Annoyingly Jamie Bamber. Battlestar Galactica using a sort of US accent was acceptable as I did not know then he was a Brit. Eventually he started in the beginning of the Brit Version of Law and order with I assume his natural accent but horribly for me was the sounds he made in the series Body Of Proof. His run did not last long but what is is to hear a Brit faking an accent that is meant to be English anyway. I also hate it when non IRISH SCOTS attempt those accents and mix the two. Same with Northern and Southern Irish accents get muddled by one character. However I beleive all of that can be forgiven if you watch How Green Was My valley. Allegedly the US who gave it a few Oscars were happy to believe everyone spoke with a Welsh accent even though it came across as Scottish Irish for many. With Welsh having one of the most ear pleasant musical sounding accent, perhaps the nicest in Britain this must have stuck in some craws.
Jason just tries to sound somewhat malevolent and dangerous. Even when trying to endear himself I think.