One of the doctors should take a leap of faith, there have been plenty that did it in the USA, and its still federally illegal.
No one wants to be the first.
And yes the UK government cultivate Cannabis in Hackey, London as well as in Bury St Edmunds. They extract parts of the plant to make their synthetic version called Sativex, which has had the majority of the Cannabanoids removed. Thats another story though.