I too was surprised to see the Typhoon beating up STN earlier today and was wondering why. Now I know! Presumably the last time that pax will ever set foot in a commercial aircraft.
Regarding your comment HD, if the 'disruptive pax' situation developed into a hijack situation and the aircraft took a turn towards central London then the Typhoon would be there, ready to do what was necessary. Nobody wants another 9-11 and a failure to react would not be acceptable second time round.