This is not to give excuses, but one might be a little more forgiving to outsiders (Americans who say that, at least) when you remember that 82% of the population of the UK lives in England.
12%, incidentally, of that, lives in the London area. Give or take.
I'm not making excuses for the English, though. Sometimes (as an outsider) I get the hint that it may go deeper than just a slip of the tongue.
DOES it go deeper than just an innocent slip of the tongue? Give me some inside stuff. :)