You've misread the legislation. The maximum sentences you're referring to are for summary convictions at a magistrates court. Possession of a controlled substance is an each-way offence which can be tried at either a magistrates or crown court. There is a higher maximum sentence if your offence is tried at a crown court, which is listed in schedule 4, namely "5 years or a fine, or both".
But that law has to be read in conjunction with others, which set out when trial is at magistrates or crown court; and what the sentencing guidance is.
The courts must follow the sentencing council guidelines unless it's in the public interest not to do so.
Judges don't have to adhere to guidelines as these are only guidelines. I have seen couple of cases where people were punished severely for something rather minor. Only thing you can do is to complaint about the judging.
> The primary role of the Council is to issue guidelines on sentencing which the courts must follow unless it is in the interests of justice not to do so.
> The Sentencing Council is an independent, non-departmental public body of the Ministry of Justice and replaced the Sentencing Guidelines Council and the Sentencing Advisory Panel in April 2010.
