In 2018, UK cannabis law changed through an update to the Misuse of Drugs...

https://zionsniceinsight.readspirex.com/posts/why-does-uk-drug-law-use-both-classes-and-schedules

In 2018, UK cannabis law changed through an update to the Misuse of Drugs Regulations 2001, not the Misuse of Drugs Act 1971. This allowed specialist doctors to legally prescribe cannabis-based medicines like Sativex and Epidyolex