I may be missing something here but had the captain signed for the aircraft or were the doors closed. If not they are only guilty of thinking about going flying. You cant be done for drink driving unless youve started driving, just prevented from following thru an error of judgement.
Reminds me of the duty decoy in the car park joke.
Go to any hotel with crew in it and there are off duty crew boozing. Right or wrong its a fact, so lets stop making out its confined to BA.