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

https://dlf-ne.org/what-international-treaties-affect-uk-cannabis-law/

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 prescribe cannabis-based medicines like Sativex and Epidyolex