Today’s cannabis debate shows how irrational Westminster has become

This afternoon, a handful of MPs will gather in Westminster Hall to debate cannabis policy. It's like sending a policeman out to fight an invading army. We are witnessing a policy failure of epic proportions, and the debate parliament holds – one it has been forced to hold by public petition – will be conducted with a handful of MPs in a legislative attic.

Cannabis is the great snickering joke of drug laws, which are in themselves a disaster. The failure of attempts to control it over the last 50 years means it is socially very widely accepted and available almost everywhere. If you live in a city, you will have inevitably smelt it on the street recently. Nearly 30% of Brits will try it at some point in their lifetime. Nearly four per cent of 16-to-59-year-olds tried it last month alone.

And yet it remains illegal, with potentially harsh sanctions for those caught with it. Tens of thousands of people receive some form of punishment for cannabis every year, from official warnings at the bottom end to jail time at the top end. For many, cannabis gives them a criminal record which cripples their employment prospects in the future. Others – disproportionately blacks and Asians – experience the brutality of the penal system. For others, a cannabis warning from the police constitutes their first contact with the authorities and triggers a lifetime of distrust.

And yet you wouldn’t know how categorically and tragically the drug war had failed from the government response to today's debate. Some 220,000 people signed a petition demanding the debate – far above the 100,000 needed to trigger a possible debate in the Commons. The government response was to put out a statement ruling out any change of policy and chuck the debate into Westminster Hall.

The MPs responding to constituents' letters on the matter have issued the most banal recital of Home Office argument imaginable. There is no evidence whatsoever of independent thought. But at least they have the excuse of lack of interest or comprehension. The most severe criticism must be reserved for those who understand and do nothing. That includes nearly every leader of a mainstream political party, because one of the weird secrets of the drug war is that we are governed almost exclusively by cowardly drug reformers.

Jeremy Corbyn believes "the cannabis battle in the war against drugs is being lost". David Cameron believes it would be "disappointing" if radical options on cannabis law weren't pursued. Tim Farron believes "the war on drugs must end". Nigel Farage believes "the war on drugs was lost many, many years ago and that the lives of millions of people in Britain are being made miserable by the huge criminal element that surrounds the illicit drugs trade".

Or at least, they believe those things until they attain power, and then they change their tune. Of these men, only Farron has really followed through, although Farage deserves credit for making the case to a party unlikely to agree with him. Having gone into the last election pledging radical drug reform, the Lib Dems are today announcing the establishment of a panel on how to create a legal market in cannabis. It's a rare instance of courage in a cowardly debate. Everyone else remains terrified of a presumed tabloid backlash. That's why the first thing Gordon Brown did when he became prime minister was give in to Mail editor Paul Dacre's demands and reclassify cannabis as Class B, despite there being no evidence whatsoever of harm.

But the tabloid backlash is largely mythical. The Sun has already been convinced of the case for drug reform. Like Corbyn and the home affairs select committee, it recommends a royal commission on the current law. Only the Mail holds out. But it does so in a manner which says more about the whims of its editor than the views of its readers. An Ipsos Mori poll from 2013 showed 53% of the public support the legal regulation or decriminalisation of cannabis. Forty-five per cent of Mail readers agree with them.

Ask Cameron what he thinks of drugs now and all the usual cut-and-paste nonsense comes streaming out his mouth. His previous convictions have magically disappeared. Instead, he repeats the Home Office mantra that drug use is falling due to their policies and that this would be the worst time to change course.

And it’s true that cannabis use has been falling. We're not sure why, but it’s certainly not because of prohibition. The downward trend started when cannabis was reduced to Class C and continued after it changed to Class B. Most of the sensible people in the debate (including in government) presume it is connected to the fall in smoking in general. Joints, which usually also have some tobacco in them, are probably being viewed by younger users with the same distaste as cigarettes.

But even this trend relates to between 2003 and 2010 – not 2015. Over the last few years, use has been largely flat at between six and seven per cent of the population. The rate of youth cannabis use stands at 16.3% – about the same as last year. The government's own data suggests that the fall in drug use "has gradually stabilised".

If tough laws led to a decline in drug use, we wouldn't be witnessing a rise in the use of ecstasy and cocaine or a dramatic rise in illegal drug-related deaths. The Home Office's own international comparators report found:

"We did not in our fact-finding observe any obvious relationship between the toughness of a country's enforcement against drug possession, and levels of drug use in that country."

The Netherlands, which allows open cannabis use, has lower rates than in the UK. And the places around the world which are experimenting with regulated cannabis are finding that all the fear-mongering has been inaccurate.

Alaska, Colorado, Oregon and Washington have legalised non-medicinal cannabis use, with retail shops opening in Colorado and Washington last year and Oregon last week. The evidence from Colorado is that there has been no spike in cannabis use or increase in road accidents. The tax take for 2015 is predicted to be $125 million (£81 million). And that's not to count the economic benefits of citizens who have not received a criminal record for taking a drug which has proved immensely popular and largely safe over the last half a century.

The government won’t do research into the effect of a cannabis market in the UK, but the best quality data suggests we would save between £200 million and £300 million annually across the criminal justice system, generate between £400 million and £900 million in tax revenue, contribute to a reduction in the government deficit of between £0.5 billion to £1.25 billion per year and only incur costs of £85 million.

But few MPs can countenance such an obviously rational and healthy development. Out of some barely-existent tabloid threat, they turn their back on a policy which could generate revenue, improve health outcomes, and save thousands of young people from a criminal record.

The chasm between the reality of cannabis law and the political debate about it shows how disconnected our political class has become from reason. Evidence and logic do not matter, only the supposed instincts of the tabloids. It is a terrible mixture of anaemia, risk-aversion and moral relativism.

Today's poor excuse for a debate throws that failure into sharp relief. But the MPs who laugh off their own youthful indiscretions with cannabis are not the victims of their policy. It is the young people of today – especially the black and Asian young people – who are its primary victims.