Medical cannabis is legal, but road safety rules remain strict. The 2mcg/L THC...

https://hotel-wiki.win/index.php/Is_the_UK_Basically_Zero_Tolerance_for_THC_When_Driving%3F

Medical cannabis is legal, but road safety rules remain strict. The 2mcg/L THC limit applies even with a medical defence, and DVLA fitness standards must be met. Remember: legality is not a substitute for responsibility