This thread’s an interesting read, so interesting that I did a bit of digging and i think this makes it quite clear:
gov.uk/government/collectio … and-limits
As the law stands it appears to be an offence to drive any motor vehicle whilst you have more than 2µg of cannabis per litre of blood. I guess that this law mas made before prescription cannabis became a thing and the limit may well be revised to reflect this at some point in the future. The way I read it this limit applies right now for anyone.
It is interesting to note that limits are also stated for other prescription medicines which have been mentioned here and it appears that these limits apply whether the med it prescribed for that person or whether it is being used illegally.
Make of it what you will but I doubt that the OP will be (or indeed is) driving legally. Sorry but I think it’s better to know now than find out the hard way in future.