In 2018, UK cannabis law changed through an update to the Misuse of Drugs...
https://charlie-wiki.win/index.php/If_Drug_Control_Is_Reserved,_What_Can_Devolved_Governments_Change%3F
In 2018, UK cannabis law changed through an update to the Misuse of Drugs Regulations 2001, not the Misuse of Drugs Act 1971