Like Guest,Van I wondered what practical help the Typhoon could offer had the hijack been genuine.

Close-up eyes on the spot I suppose, plus the ability to bring it down if a serious threat to a ground installation were to develop (as in "We have a bomb on board, and are above GCHQ Cheltenham, or the lines in Hereford, or Bristol city centre"). Such actions would be of little help to the chopper itself, but might be contemplated for the greater good.

I am unsure how much time going supersonic will have gained, maybe 5 minutes, but the hoo-ha about it will doubtless help keep up the public level of anxiety about terrorism.