So just to summarise what you're saying BJCC, just so you don't receive any undue criticism.
Passengers are kept secured onboard the diverted aircraft, potentially sitting on a semtex seat cushion, rather than being allowed to disembark/evacuate because of the potential risk of one or more terrorists running amok airside with whatever they managed to smuggle aboard.
Now if this is the case at least there was some logic behind the decision, perhaps flawed logic but not paralysis.
However, the risk assessment does seem a little skewed as I assume the aircraft in question is parked on the most remote stand at the airport and any running amok would be easy to isolate, even with the existing airport police before the cavalry arrive from Glasgow.