With regards to David Learmont's comments...
Are they as complete rubbish as I think they are?
Surely if the Cabin Crew tell the Captain that someone has an explosive vest on then as the Captain you would have to trust the Cabin Crew's competency and take the threat seriously (i.e. do what the hijacker wants?).
Presumably, the Captain would never even see the hijacker?
And try telling relatives of victims of Metrojet that it's "impossible" to get explosives onto a plane...