In reply to Michael Gordon:
For example the official stats:
http://www.theguardian.com/news/datablog/2012/sep/28/drug-use-age-popular-c...
My honest view is that official stats must be seriously underestimating rare use (once only, a few times only, used modreately for a short period etc). Most of my friends always said they never used drugs if asked, as the risk of consequencies were high. Its also terrible politics to admit the scope of the problem as it shows the war on drugs just doesn't work and the population tolerates uncontrolled substances and the criminal gangs usually behind them, becuase the government won't do something more sensible.