In 2018, the UK amended the Misuse of Drugs Regulations 2001—not the 1971...

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

In 2018, the UK amended the Misuse of Drugs Regulations 2001—not the 1971 Act—to allow certain cannabis-based medicines like Sativex and Epidyolex by prescription. These remain Class B drugs, prescribed only by specialist doctors under strict rules