Farty - yes, you are missing something.....intent.
The very fact that they turned up to work is good enough evidence in the eyes of British Law, as Rowardennan correctly mentions with regard to drinking and driving.
The crew (if the allegations are true), would have been better off pulling a sicky. (I know of no one who has turned up to work, in uniform, with the intention reporting in sick - and if it was these guys' intention, they'll struggle to prove it...)
Let's face it we all know it happens and is certainly not confined to BA, unfortunately for them, got caught.....