Yeah, being a Brit too I seriously can't stand the accent. 99% of the people don't talk in that way. Aside from anything else though, it's not even an accurate stereotypical accent. It seems inconsistent - often dipping into an Australian and even South African accent. This makes me think that the character is putting on the accent. Perhaps he is actually Aussie, Kiwi or South African...
EDIT: To back up my point listen to the way he says 'No, just that one' when
Michael asks him if he has any other weapons. That's not an English accent. Whether it's the actor or the character, that sounds very South African/Kiwi (they are similar accents).