"HOw on earth did they get through security with that I thought!"
Jockflyer,
Whilst I understand your concerns I think you will probably find that they didn't get through security with the glass but purchased the Pint in the Airside bar then boarded your flight.
Boarding is usually handled by the Handling Agent and I am quite sure they would not have let someone onto the Apron holding a Pint, oh and don't CC greet pax and check boarding cards on the way onto the AC, surely they would of noticed this at that stage.
LDY - DUB is usually operated by the SF340, not many seats on this AC so surely the CC would of noticed this person consuming the Black Stuff on board??
Incidently you can purchase up to 5 yes thats 5 LTRs of Spirits at the Duty Free to take on board.
I think your gripe may be with Transec and not Security in this case.
I don't know if you have ever visited BFS but just before the search area there is a gift shop and they will happily sell you any Gods ammount of Guinness Glasses to take home as a momento.