Set a limit - say 35mg (same as driving limit).
If you test positive, you don't board and get a £500 fixed penalty and a 3 month passport ban, If you cause trouble onboard and test positive on arrival, you get a fixed penalty £500 and 3 month passport ban plus any additional charges.
It'll never happen because the profit made on alcohol sales outweighs the perceived risks, agree with station_calling, airport alcohol sales in the EU are often more expensive than supermarkets - What's the point?
Agree with Piltdown, you're not trying to educate the perpetrators, you're making anyone who follows think twice before getting on a plane pi$$ed.