Legal medical cannabis isn't a free pass. You’re still bound by the 2μg/L THC...

https://evpowered.co.uk/feature/medical-cannabis-and-uk-driving-laws-what-ev-owners-must-know/

Legal medical cannabis isn't a free pass. You’re still bound by the 2μg/L THC limit and DVLA fitness standards. While a medical defence exists, it doesn’t override impairment. Legality never replaces your primary duty to ensure you’re safe to drive.