Since all else are derivatives isn't British English the standard?
I would go with whatever got the message across most effectively. I'm pretty certain that shows like the BBC have certain standards of acceptable dialog. And some of them must include using a more internationally acceptable version of English. CNN has guidelines including lists of words that can't be used, so I would be surprised if the BBC didn't.
I once published a magazine for an international audience and the copy editor was English. She just said at the beginning. OK we will use American English. There were only a few instances of figures of speech where the English and American versions were completely different. Otherwise it's mostly spelling and vocabulary. Of course the humor is completely different...
Come to think of it, whenever we used English writers they always submitted American English as well.