The courts must follow the sentencing council guidelines unless it's in the public interest not to do so.
https://www.sentencingcouncil.org.uk/wp-content/uploads/Drug...
The starting point is 100% of weekly income; the range is 75% to 125% of weekly income.
> Band B 100% of relevant weekly income 75–125% of relevant weekly income
https://www.sentencingcouncil.org.uk/about-us/
> 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.