I feel for the controllers who were, I gues, just the guys in the middle.
I have been in a very similar situation of having to tell the pilot of an airlines full of pax that he has to divert or would be shot down and it is very, very difficult to balance professionalism and a desire to help the crew with the demands of an outside agency. In my case I was not helped by having a maching gun stuck in my ear as the pilot laughed and said "You must be joking; we're carrying on!" Eventually the message got through that it wasn't a joke and the aircraft landed as instructed.
(So far as I recall this was NOT during my time at Heathrow!)