EV drivers using medical cannabis have a legal defence against the 2mcg/L THC...

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

EV drivers using medical cannabis have a legal defence against the 2mcg/L THC limit, but fitness to drive is paramount. Legality doesn't replace responsibility; impairment is still a liability