Not surprised, actually.

Never been to the UK, but every place has kids who get bored and need to do something slightly rebellious to find themselves and feel like they're cutting against the grain for their own independence. Peer pressure also plays a role.

In the US, kids usually do this either by playing pranks or exploring places that are off-limits. Smoking and drinking will take place in more impoverished places or with someone who has connections (or a careless parent).

In the UK, particularly in densely populated areas like London, it seems like the youth who get bored or need something to do usually turn to drinking and narcotics because it attracts less attention (and police) than destroying someone's property. Not saying property destruction doesn't happen for fun in London, but in a weird way, it makes sense to me that UK kids would try cannabis.

Maybe I'm being too stereotypical in my thinking, but gathering with your mates in a private area and passing the roll, bong or bowl around seems like....a very British thing to do.

"Oh piss off! It's not 'urtin' anyone! What, you rather we go out and steal a car or sum'fing?"