Thanks for that; it looks as though it would take 30 minutes or so to lose the 50 tonnes, thus spreading the fuel twice as far as my rough guess above, assuming the aircraft wasn't circling....
So, in the case of this LHR-CWL positioning flight, if it was done at all was it done on route, over the sea, or somewhere specially designated?
Does anyone know?
There's no news story here; 250 Kg per mile, as a mist at altitude, is not significant. I'm merely curous, and not a journalist in the first place.