Alot of kids like to be seen drinking because they know they're underage and think it makes them cool. Even though the legal drinking age in the UK is still much lower, all the 14 year olds think they're the shit. They sneak alcohol into school and everyone is like 'WOOOO, IT'S NOT ALLOWED.. SO AWESOME!'
In general, people make too much of a show, being proud of drunken revelry or a slave to the liquor. It's so ingrained in UK culture it's not even funny. I think for alot of people that don't smoke pot or anything there is still that novelty of using a mind altering substance, and although its legal they act like it's not or do something illegal.
I think the novelty of cannabis will wear off because of the medicinal applications. Boring people smoke pot too, so it;s not cool.