OOT:
A little naive aren't you? If the airliner intercepted is not found to be operating normally and hijacked by terrorists then guess what's coming next!
The UK government will authorise the aircraft to be shot down and regrettably that order will be carried out.
No waving is going to happen.. 
Naive? How different from 'normal' does a Heathrow bound ac have to fly, it's not easy in a very short time frame to determine 'terrorists' have taken over a suspicious ac..................... and as for getting that decision to shoot down a civilian airliner from a high ranking goverment minister. I wonder............