The law regarding Hash, Pot, solids, marujuana, whichever name you know it by has been altered quite a lot of late. It used to stand at if you were in possession of an ounce, then it could be claimed to be for personal use, over this and you would be charged with possession and possession with intent to supply, which would then have to be proved. In respect of growing the stuff you were allowed approx 3 plants before you could be charged with cultivating and intent to supply. First offenders dependant on quantity would usually get a slap on the wrist, confiscation of related paraphernalia and any monies deemed to be gained from illicit gain would also be confiscated, along with a fine.
The Class A drugs as already stated carry a heftier fine and custodial sentence subject to probation reports, Although many judges for first offences will rely on the probabtion report and see whether or not a rehabilitation order over custodial is more appropriate.
Obviously repeat offenders and those higher up the scale ie those dealing in vast amounts would be taken off the streets and dependant on whether or not previous orders have been made and the severity of the offence, would depend on what sentence was issued. I have known repeat offenders to be given 10 years plus for trafficking/dealing.
In all honesty, not getting involved in the first place is the best advice anyone could give, regardless of whether or not you feel certain drugs should be legalised, until such a time, keeping clear is the best policy, that way you can avoid any police involvement at all and sentencing wouldnt be a concern