I'm native English speaker and to me his accent is a classic mid-Atlantic, and it can sometimes veer towards more British or more American, probably depending on where he is, and who he's talking to. Sometimes he sounds very British, even using the glottal stop (missing the 't' out) which is quite London, other times he has a definite American twang and intonation.
As a former languages teacher all I can say is, he is a fantastic role model for British youngsters, as we are famously rubbish as a nation in this department and language teachers in Britain really have a hard time trying to get across to children the importance of trying to speak another language and not being afraid to have a go..
So good on yer Mika!