Evidence is mounting that our drugs laws are not working.

New analysis from Release and the London School of Economics shows beyond doubt that the way in which they are implemented is highly discriminatory, ineffective, and counterproductive. Hundreds of millions of pounds of taxpayers’ money are spent every year on arresting and processing people for possessing drugs, with no discernible impact on drug markets or levels of use. Meanwhile, thousands of otherwise law-abiding people receive criminal records, and many poor and minority communities deal daily with the feeling that the police are unfairly targeting them.

The Release/LSE report makes a persuasive case that the main reason police forces remain addicted to low-level drug policing (172,400 people were dealt with by the police in 2010 for possession of drugs – a 235 per cent increase over the previous 10 years), is that they give beat officers and managers an easy route to hitting targets for “solved” crimes. But perhaps the more damaging impact of all this is on police-community relations. The research finds that only 7 per cent of the 550,000 stop-and-searches carried out in 2010 resulted in an arrest, and these intrusions into personal privacy were overwhelmingly targeted at young, poor, ethnic- minority males.

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The Government claims that the existing drug policy is working, and indeed there are some encouraging results – HIV infection among drug users remains low, thanks to our early implementation of harm- reduction programmes from the 1980s onwards. We have world-leading treatment and recovery services, and are helping more and more people recover from addiction. Intelligence-led policing has held drug market-related violence to relatively low levels.

But these successes mask an inconvenient truth – that the element of drug policy in which political leaders have put most faith (the deterrence of potential users through the threat of arrest and punishment) has contributed little if anything to this progress, and entails massive financial and social costs. We have seen in recent years a significant fall in cannabis use, but rises in the use of many new synthetic substances. Supporting the Release/LSE argument that these trends have nothing to do with the deterrent effect of arrests, the most significant drops in cannabis use occurred between 2004 and 2009, when cannabis was temporarily downgraded to a Class-C drug.

Both of us have been involved in the politics and implementation of drug policy for many years and, like most people, know that it is a complex problem with no simple answers. It is not just about being “tough” or “soft”, or looking for the next eye-catching solution. But when the clear evidence and years of experience shows that a particular strategy is producing more harm than good, any sensible government would conduct a review, in order to find a more cost-effective approach.

Mike Trace is a former deputy drugs czar; Caroline Lucas is a Green Party MP