In 2018, UK cannabis law was updated through changes to the Misuse of Drugs...
https://collinnfmn145.theburnward.com/i-thought-cannabis-was-legal-in-the-uk-why-can-i-still-be-arrested
In 2018, UK cannabis law was updated through changes to the Misuse of Drugs Regulations 2001, not the Misuse of Drugs Act 1971