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

https://touch-wiki.win/index.php/Does_Having_a_Private_Prescription_Stop_Cannabis_Being_Illegal%3F

In 2018, UK law changed the Misuse of Drugs Regulations 2001—not the 1971 Act—to allow specialist doctors to prescribe cannabis-based medicines like Sativex and Epidyolex