UK cannabis law changed in 2018 with an update to the Misuse of Drugs...

https://www.tntmagazine.com/leisure-entertainment/leisure/why-is-cannabis-still-illegal-in-the-uk-the-history-behind-medical-cannabis-law/

UK cannabis law changed in 2018 with an update to the Misuse of Drugs Regulations 2001, not the older 1971 Act. This allowed specialist doctors to prescribe cannabis-based medicines listed under Schedule 2