Alicia Castilla was 66 years old when she went to jail.

The kindly, mild-mannered Uruguayan lets her glasses hang around her chest as she explains that she had 29 small cannabis plants in her garden.

She had cultivated the plant to help her sleep. In response, armed police invaded her home. She was put in jail for 95 days.

"There are no words to describe the prison in Canelones," she said. "There are cockroaches everywhere - in the bed, everywhere. Everything you touch is covered in cockroaches. The bathrooms were beyond filthy and the rats were the size of a weasel."

Was this the injustice which moved the UN to criticise Uruguay yesterday? Or was it the $30 million (£18 million) the tiny South American country spends on those in jail on drug charges? Or the fact that Uruguay has more deaths through drug trafficking than addiction?

No. The UN criticised Uruguay yesterday because it legalised the use of cannabis. Amid all the wasted money and human potential of the war on drugs, that is the move which the UN's International Narcotics Control Board annual report singled out for criticism.

"INCB is concerned about some initiatives aimed at the legalisation of the non-medical and non-scientific use of cannabis," it found.

"Such initiatives, if pursued, would pose a grave danger to public health and well being."

Then, threateningly, it added: "INCB looks forward to maintaining an ongoing dialogue with all countries, including those where such misguided initiatives are being pursued, with a view to ensuring the full implementation of the convention and protecting public health."

It's just the latest threat from the UN's bully organisation, which polices national states' drug laws to ensure they remain counter-productive.

Just before the Uruguay parliament voted to legalise cannabis use, a note was sent through the permanent mission of Uruguay before the United Nations in Vienna threatening it with the consequences of its decision.

"The board would like to reiterate that the planned legislation on cannabis, if approved, would constitute a violation of the treaties on international drug control, in particular the 1961 Convention, which would impact the international solidarity in the fight against drugs," the note read.

"Therefore, it urges your government to cooperate with her in this matter and, in particular, to accept to receive the proposed mission which would be headed by Mr Raymond Yans, president of INCB."

The message was unmistakeable. It goes without saying that no similar threats were made to Colorado and Washington, two US states with individually higher populations than Uruguay which both recently legalised cannabis.

"Do they have two discourses, one for Uruguay and another for those who are strong?" left wing Uruguay president José Alberto "Pepe" Mujica Cordano asked.

For half a century, the INCB has been blind to its own failures and virulent in its enforcement of international drug policy. Even as it hides under the benign banner of the UN, it enforces instability, violence and wasted lives through its tunnel vision on drugs.

It's been this way throughout its history. Back in 1962, a year after the SIngle Convention on drugs was passed enforcing draconian drug laws across the world, it was boasting of its new found power.

"All non-medical use of narcotic drugs, such as opium smoking, opium eating, consumption of cannabis (hashish, marijuana) and chewing of coca leaves, will be outlawed everywhere," it said.

"This is a goal which workers in international narcotics control all over the world have striven to achieve for half a century."

That was 52 years ago. What has it achieved in that time?

Its report yesterday noted that "unprecedented" numbers and varieties of new psychoactive substances were appearing across the world. Central America and the Caribbean "continue to be affected by drug trafficking and high levels of drug-related violence", while "large-scale illicit methamphetamine manufacture" goes on. It reported an overall increase in the trafficking of opiates through Africa, including a ten-fold increase in heroin seizures in east Africa. Heroin manufacture and demand continued to rise in east and south-east Asia. Opium poppy cultivation in Afghanistan hit new records, with a 39% increase in 2013. The illegal cultivation of cannabis at home and in large plantations continued to increase in Europe.

It is as comprehensive an admission of defeat as could be imagined. Half a century later, and the policy the Single Convention enforced continues to make the world's drug problem worse. But instead of thinking again the INCB attacks those who try something new. The human mind is capable of extraordinary levels of self-deception, but the INCB deserves a special mention for its ability to list its own failures and then react angrily when anyone suggests an alternative.

Essential to its bullying is the implication that any state bowing out the Single Convention is breaking the terms of the treaty. This is almost certainly an empty threat.

The treaty does force parties to pass laws carrying out its provisions - such as the UK's Misuse of Drugs Act 1971 and the US' Controlled Substances Act of 1970, both of which were designed to fulfil treaty obligations. But it is far from clear if that extends to the criminalisation of personal use. The threats against cannabis legalisation laws are a power grab.

The INCB has tried to turn this treaty into a holy commandment, a stone tablet brought down from on high. It refuses to countenance any reform on the basis of new evidence or even the simple, unchallengeable fact - one implicitly admitted by its own report - that the war on drugs is failing.

A forthcoming report from the Transnational Institute and the Global Drug Policy Observatory is expected to show that the inclusion of cannabis in the Single Convention was the result of political compromise rather than scientific backing. How many young lives have been wasted in jail because of that compromise? How wilfully blind must an organisation be to not see the damage it does to countries across the world, in the north and the south, by refusing to think again?

They know the tide is turning. With the wind in their sales, drug law reformers are preparing for the high-level UN drug policy meetings in Vienna later this month and another in 2016, when meetings will be held on prohibition and potential alternatives. Nick Clegg is working to have a common European position on reform ready by then.

This is the INCB's attempt to scare countries - particularly poor countries - to keep them in line. They are scared that any moment now this appalling experiment will be shown for what it really is: an affront to individual liberty, global stability and public health.

Ian Dunt is editor of Politics.co.uk

The opinions in Politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.