With America rethinking its policy on drugs, our MPs and MEPs need to make their own feelings known

It was with great foresight that a Conservative backbench MP stood up during a parliamentary debate in the House of Commons in 2002 and pleaded with the then Labour government to rethink its commitment to the "war on drugs". "I ask the Labour government not to return to retribution and war on drugs. That has been tried and we all know that it does not work."

Contributions like this have been all too rare from British politicians, particularly at a time when the debate about the merits of prohibition has changed so radically in recent years. That is most evident in the Americas, both North and South.

Over the past five years, Latin American support for the "war on drugs" has ebbed away. The so-called "drug-producing" nations have tired of bearing the brunt of the violence as they attempt to eliminate the supply of drugs to the "drug-consuming" nations to the north.

In Latin America the war on drugs presents a different order of threat than that posed in the US and Europe. The threat is an existential one because prohibition has the effect of driving profits and power into the hands of murderous cartels. They corrupt, challenge and often destroy the institutions of the state – the police, the judiciary and the body politic. Colombia very nearly succumbed to the cartels during a decade when drug-related violence tore the heart out of the institutions of the state and left many civilians dead. Politicians, public prosecutors and members of the judiciary were ruthlessly targeted. Many of the politicians who escaped death only did so because they were in the pay of the cartels. Welcome to the war on drugs.

Guatemala and Honduras are the new battle spaces, facing exactly the same challenges as Colombia did. No wonder Latin Americans are tired of paying such a high price. In recent years the presidents of Colombia and Guatemala – and international bodies and reports such as the Organisation of America States and the Global Commission on Drug Policy – are speaking with one voice: the war on drugs can never be won; we need to look at alternatives.

And while prohibition in the west poses its own challenges and creates its own misery, it is not a threat to the very fabric of the state. But since their citizens – largely – create the demand that fuels the war on drugs they have a moral responsibility that they have shamefully failed to acknowledge.

But the debate is changing in North America – as Kasia Malinowska-Sempruch makes clear in other pages today – and public opinion is driving significant policy changes. American states are introducing – or considering – a licensed, regulated market for marijuana. Since January, people can buy marijuana in Colorado for recreational purposes. Washington State will soon follow suit.

An indication of the new direction of travel came last month at the World Economic Forum when the Republican Texas governor Rick Perry said: "After 40 years of the war on drugs, I can't change what happened in the past. What I can do as the governor of the second largest state in the nation is to implement policies that start us toward a decriminalisation and keeps people from going to prison and destroying their lives, and that's what we've done over the last decade."

Last October, the head of the US Justice Department, Eric Holder, said: "As the so-called 'war on drugs' enters its fifth decade, we need to ask whether it, and the approaches that comprise it, have been truly effective… Today, a vicious cycle of poverty, criminality and incarceration traps too many Americans and weakens too many communities."

But in Britain we have heard nothing from frontline political figures. Until now, which is why Nick Clegg's intervention is a welcome one and may start a debate on the merits or otherwise of the war on drugs.

The onus is on those who support prohibition to make the case for prolonging a war that has evidently failed. Political figures in the UK and Europe need to engage with the changing tide of public opinion in the Americas and investigate whether market alternatives may provide a better solution than prohibition.

Perhaps the Conservative backbencher who entered the debate in 2002 and declared the war on drugs a failure would care to re-enter the debate? Especially as he is now the prime minister.