<<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. >>
There aren't too many places, if any, on air routes in southern England where it would be "safe" to shoot down a commercial airliner. If it took place anywhere close to London the carnage would be horrendous. There is a way for the pilot to communicate to ATC various stages of emergency so it would be interesting to know if that occurred, although I doubt we shall ever know.