With all due respect, I can't see the sense in such a policy.

I'm assuming that BA management are totally opposed to the practice of alcohol being removed from their lounges. So .... that being the case, there needs to be some form of clear deterrent if there is any wish to stop it becoming a frequent event.

However, the idea that - if caught - the worst that can happen is that you would be asked to pay is no deterrent at all. In fact it almost encourages theft, in the knowledge that you can cough up the cash and walk away with no sense of guilt or shame : all a dramatic contrast to a potential lounge ban - and the strong message it would send out to anyone thinking along similar lines.