Drug treatment policy needs a dose of evidence
So all good citizens this week are poring over the Programme for Government, and it's true that there is much to be pleased with. Labour wasn't all about unbridled credit and fun public sector spending sprees: they kept all your emails, kept records of the websites you visited, used "anti-terrorism" legislation on people who plainly weren't terrorists, and so on.

But most interesting are the noises being made about crime and evidence. "We will conduct a full review of sentencing policy," they say, "to ensure that it is effective in deterring crime, protecting the public, punishing offenders and cutting reoffending. In particular, we will ensure that sentencing for drug use helps offenders come off drugs."

These are grand promises. Compulsory addiction rehabilitation with drug testing and treatment orders was introduced 10 years ago as an alternative to custodial sentences or probation for drug-related crimes. Their implementation without adequate analysis is one graphic example of our ineptitude at running simple trials of social policy.

A judge making a decision on a criminal's sentence is in the same position as a doctor making a decision on a patient's treatment: they are choosing an intervention for an individual with the intention of producing a particular set of positive outcomes (reduced crime, and reduced drug use). They both get through a large number of individuals in a month; and in many important situations they don't yet know what works.

If you randomly assign a fairly large number of criminals, or patients, to one of two interventions and measure how well they're doing a year or so later, you discover which intervention is best. Add in the cost and you know which is most cost effective.

Before being rolled out nationally in October 2000, drug orders were extensively piloted in three cities by the criminal policy research unit of London South Bank University.

What insights did this generate? There was no randomisation, and no control group of identical criminals given traditional sentences for comparison, so the only new knowledge generated was the revelation that it is possible to set up a DTTO service and run it in some buildings in some cities.

When they did follow up the people who had passed through the service, they hadn't done particularly well. But the chosen study design means we have no idea how these participants would have turned out if given a custodial sentence.

This is a tragedy, and not just because drug use is estimated – with the usual caveats on estimating nebulous notions – to cause 85% of shoplifting, 80% of domestic burglaries, over half of all robberies, and so on. This is a tragedy because it speaks to motives that will never go away.

It takes a brave politician to say "I want to introduce a new policy, but I don't know if it will work", to try it out on half of a group of people, and measure their outcomes years later, perhaps after the politician has moved on.

This would revolutionise social policy and if Cameron and Clegg were really young and visionary, they would step up to the plate.

Unthinkable? Repeal drugs laws
The government has invited us all to nominate legislation to be repealed. Where better to start than the Misuse of Drugs Act. Across Whitehall and in the medical profession, making a fresh start on the regulatory framework for drugs is probably the one thing discussed with the least publicity and the most fervour. In March, a former No 10 policy analyst, David Halpern, came out in favour of legalising heroin. The previous October, the government's chief drugs adviser, David Nutt, was sacked for arguing that some illegal drugs were less dangerous than alcohol, having already pointed out that the Home Office's precautionary principle simply made some drugs look more attractive. And it is a decade or more since the new international development minister, Alan Duncan, called for legalisation in his book Satan's Children. Mr Duncan approached the problem as a devotee of the free market. The less ideological tackle it by trying to assess the harm – the impact on law and order of drug-related crime, for example, which accounts for four-fifths of offences like mugging and burglary. And while it was perhaps ill-advised for Professor Nutt to point out that as many deaths are related to horse riding – relatively easy to ban – as to harder-to-track illegal ecstasy use, it does not make it less true. In Britain and America, the war on drugs is now widely seen as a failure. Begin again by treating drug abuse like alcoholism and smoking – not as a matter of law and order but a question of public health.