Agreed. Legalise, regulate and tax it as per tobacco and alcohol.
Then focus policing on the black market sellers - who when caught can be slammed with double whammy charges of unlicensed distribution and avoiding HMRC & Import / Excise duties, the latter of which should see them in chokey until the next millennia.
With tobacco tax take nose-diving the cannabis taxes would surely be most welcome by HM Treasury. The police would also appreciate it I'm sure - they have better things to do than wasting time cautioning or prosecuting endless piles of people who have a tiny amount found in their possession.
I can't see any of the above coming to pass unless we somehow get a Liberal or Independent dominated Parliament. The rest all seem far too concerned that someone somewhere might be enjoying themselves and that really ought to be stamped out in order to best chase the wet dream of eternal and exponential "growth".
Not a partaker of the stuff myself but the above would really seem the most sane approach at this point.