That the government will allow a few serious epilepsy and multiple sclerosis sufferers to get cannabidiol medicine to relieve their symptoms is good news. That is all that can be said. Once more a decision emerges from the caverns of Britain’s NHS that reveals the evils of a politicised, centralised, deadened health service.

As it is, any cannabis medicine that contains active THC as a painkiller – as does medical marijuana for millions of people worldwide – will stay banned. Medicinal cannabis may be available across the free world. It may be available in Donald Trump’s America – where the president “backs medical cannabis 100%”. British sufferers may be able to cross the Channel and (illegally) import it. At home, it can be bought on almost every street corner, to be consumed by a reported 1.4 million Britons in pain. But British politicians love playing doctor. The health secretary, Matt Hancock, has a general election to fight. Pain must wait. He is in the grip of a cannabis taboo – and big pharma.

Every loving parent of an epileptic child knows what eases their pain. The idea that only a doctor with a prescription medicine, clinically tested by a state regulator, can measure that pain is obscene. How many heartbreaking anecdotes are needed for Whitehall to take notice? This is what happens when doctors answer to politicians who answer to pharmaceutical companies with vested interests in existing products.

When last year, the then home secretary (note, not the health secretary), Sajid Javid, issued licences for cannabis-based medicines for children in two highly publicised cases, it seemed progress was being made. But it turned out to be simply a headline-grabbing gesture. Ranks promptly closed.

Hence the welcome, if desperate, initiative last week of DrugScience, led by the neuropsychopharmacologist David Nutt, to set up a 20,000-strong trial of patient experience with medicinal cannabis. It is aimed at conditions shown to be susceptible to the drug, not just epilepsy and MS but chronic pain, anxiety, Tourette’s and post-traumatic stress. As Nutt says, it is simply wrong that ill patients in Britain should be “left untreated, in significant debt from the cost of private prescriptions, or criminalised as they are forced to turn to the black market”.

But the ultimate curse is central control over local experiment. The breakthrough in the US came when the federal government was told it could not interfere in a state’s right to decide. So in this matter of cannabis, why not set Scotland free – free to welcome Britain to the 21st century?

• Simon Jenkins is a Guardian columnist