In 2018, the UK amended the Misuse of Drugs Regulations 2001—not the 1971...
https://zandersmasterinsights.capitaljays.com/posts/i-thought-cannabis-was-legal-in-the-uk-why-can-i-still-be-arrested
In 2018, the UK amended the Misuse of Drugs Regulations 2001—not the 1971 Act—to allow specialist doctors to prescribe cannabis-based medicines like Sativex and Epidyolex