Any ATCO who tries to tell any a/c in emergency that they can't land at his/her airfield ought to be horsewhipped. Let's turn it round a little and say that ATCO A tells Mr X to go and land somewhere else. Two miles away from ATCO A's airfield, Mr X's puddle jumper develops another, more serious problem and falls from the sky to a fiery death. I don't think ATCO A would be too popular.
This sort of situation is where I (and presumably many of my fellow brethren) consider that commercial needs come second to flight safety. (You see DFC, LONDON MIL et al, I'm not such a heartless b*****d after all). Some of the London airports might feel differently though.