Although it may seem initially bathetic to put these events together, David Blunkett’s appearance before the Home Affairs Select Committee in October 2001 actually set in motion a dozen years of bickering between science and politics. Blunkett’s defining reason for reclassification of cannabis (not to incriminate young people) was eventually defied and overturned. Figures published last month show that Class B prosecutions (nearly all cannabis) had increased by about 70% since reclassification was reversed for spurious reasons by Gordon Brown in 2009.

The outcome is of much greater significance than just academic interest. The 48,000 Class B prosecutions for possesion offences last year represents an army of young people who have lost the chance of going to university or getting a visa. The drug law advice organisation, Release, estimate there have been over a million drug prosecutions in the last ten years. The question of whether we wish to inflict such limitations on achievement and happiness because of youthful temptation rarely seems to arise in public discussion or in media articles.

The All Party Parliamentary report published last week made a strong case for decriminalising possession offences following on from two other reports (Home Affairs Committee and UK Drug Policy Commission) who argued for an equivalent legal re-alignment.

It is worth recalling the reaction at the time to David Blunkett’s announcement. It was a minor affair; a small sensible adjustment in drug law backed by police and academia as a proportionate and reasonable measure. A few familiar diehard commentators wailed against further “permissiveness,” but there were so many more important issues, like global security, to worry about. In subsequent years the media profile of cannabis continued to rise until it became a punch bag for the government.

David Blunkett said, of the original reason to reclassify from B to C, “My decision was driven by the scientific evidence and the recommendation of the Advisory Council on the Misuse of Drugs (ACMD), repeated over many years (and the evidence of the All Party Commons Select Committee).

“I also appreciated this was an honest approach, which reflected much of what the police at the time were already doing in endeavouring to concentrate on Class A drug availability and the organised criminality which underpinned supply, together with an appreciation that criminalising tens of thousands of young people for possession of small amounts of cannabis was not in the interests of anyone. Too often, as we have seen since, the pendulum swings first one way and then another, but for me, education, information and proportionality are far more important in continuing the very welcome fall in usage by all age groups than bellicose chest banging.”

The full tally of the cannabis “conflict” is a depressing long list of setbacks for the integrity of drugs policy. To start with, the ACMD became politicised and haemorrhaged much of its talent following the sacking of its chair, David Nutt, and, for a while, the council of scientists teetered on the brink of intellectual bankruptcy. Although the council has regained much of its independence and authority, it long ago ceased to fulfil its statutory functions, for example it carries out practically no research and has no role in creating education messages. The last major report the ACMD published beyond a classification issue was “Hidden Harm: the children of problematic drug users” ten years ago.

The national advertising campaign on cannabis through “TalktoFrank” hugely exaggerated the mental health risks to the general population. The narrative was driven not by scientific fact but by ministerial perceptions influenced by partial news reporting by opinionated but unqualified columnists. The language and subsequent policy focus of ministers (“lethal skunk”) neglected the rapid rise of new psychostimulant drugs like mephedrone, which has considerably stronger links to addiction, overdose, and mental illness. Cannabis and mephedrone both became Class B drugs within a few months of each other, so any credibility for government funded drug messages was lost right there.

The Home Office’s determination to hog the focus of drugs policy has alienated even the police who are expected to enforce the law against young people. The top drugs cop, Chief Constable Tim Hollis, holder of the Association of Chief Police Officers’ portfolio for drugs, has suggested the governance should be wrested from the fingers of Home Office ministers and handed to the Department of Health. He said in a BBC report last week, “Enforcement alone is not the solution.”

The blunt law and order approach has also cultivated the perfect climate for the sudden demand for legal highs. The same expectations of the law simply do not apply as drug entrepreneurs have sidestepped the legislation by marketing substances as products which cannot be categorised under the Misuse of Drugs Act.

No.10 dismisses the findings of reports and detailed studies by world leading experts on drugs. But then take credit for the modest falls in prevalence in recent years. In all honesty, no one knows why some drugs are declining in popularity because there has been no research in this area, but it must be doubtful that young people are finally yielding to ministerial finger wagging.

Although prevalence of cannabis is falling, it will remain a big social and political problem so long as successive ministers seek to impose their cod science and psychology on drugs policy and cling to the idea that any “tough message” makes any difference at all.

Jeremy Sare is parliamentary adviser to the Angelus Foundation set up to educate parents and children about the dangers of “legal highs.”