As discussed previousy, yes is absolute nonsense .. has this cropped up again in Parliament Popinjay ? Can't you just see it on the night they decide no under 21's (bit like smokers and June 30th really).
Can just see John Cleese doing a sketch on this at 12 midnight. "Ok, over 21's stay where you are, over 18's form a line and march out through the pub door handing your glass to the bouncer as you exit" Life of Brian stuff ..
Will never happen.