I believe that the age limit for buying tobacco products should be raised to 21,and there should be very harsh penalties for shops etc, who break the rules.I also think there could be a good case for doing the same thing with alcohol.
Most people who smoke start young,if they havent started at 21 most wont start at all imo.
Problem is, teenage kids
will meddle with something. You only have to look at some areas in the US where they are draconian in pursuing under-age drinking - drugs take its' place. Whatever is easiest to get hold of.
I don't believe a large proportion of teenagers who drink end up having their lives ruined by it, especially if their parents are sensible about introducing them to drinking alcohol in moderation. I would wager that proportion is higher for drugs but, unlike the government, I would prefer to see scientific evidence before making such sweeping statements.

I also don't believe classification of drugs makes the slightest difference to anybody in the real world. Does a drug user have a bad day and decide it's time to make the transition from class C to class B? I don't think so. I reckon they go from substance to substance depending on what's available and what their peers are using.
The big story here is that it has highlighted what I feel has been endemic in this government for years. A total contempt for unbiased advice from the scientific / expert community in favour of making policy up according to their own prejudices and mistaken beliefs.
It has been happening in far more important areas than pot smoking too. "Climate change", energy supply, schools, the NHS, policing..... all in a mess because ministers (who are expert in nothing but canvassing public support) are "winging it".

Kevin