Being a medical cannabis patient provides a statutory defence against the 2μg/L...

https://www.bookmarking-presto.win/prescribed-cannabis-is-legal-but-roadside-reality-is-complex-you-face-a

Being a medical cannabis patient provides a statutory defence against the 2μg/L THC blood limit, but it’s no free pass. You must still meet DVLA fitness-to-drive standards