The difficulty of changing one’s mind in public means that governments persist with policies long after it has become clear they do not work. Altering course is mooted by brave souls but never properly considered. On we go, hurtling towards a dreadful mess.

In a time dominated by a hapless negotiation of a pointless enterprise, in which most other areas of policy are going by the wayside, this could be the introduction to almost any column. This week, though, like every week stretching back through governments of every complexion, it refers to drug policy.

After more than half a century of international prohibition and more than a trillion dollars spent, there are 240 million drug users. In Britain, in the past year, more than two