No supply chain is quite as lethal and destructive as that of cocaine. That was the message from the Colombian Vice-President, Francisco Santos Calderon, at a meeting of the Association of Chief Police Officers in Belfast yesterday.

Mr Calderon informed his audience that drug production is causing environmental disaster in Colombia, with illegal cultivators destroying 200,000 hectares of forest each year to produce the coca plant. But his purpose was not merely to draw our attention to this crime, but to ram home our own complicity in it. "If you snort a gram of cocaine," he said, "you are destroying four square metres of pristine rainforest."

Mr Calderon is right to point to the hypocrisy of those who claim to be environmentally conscious, yet see nothing wrong in indulging in a few lines of "blow" at the weekend. He is also justified in emphasising that anyone who takes cocaine is indirectly helping to fund brutal drug trafficking groups and human rights-abusing rebel militias which have a stake in the trade, such as the Farc in Colombia.

This is one area in which there has actually been some good news of late. Farc has been under intense pressure from the Colombian government, led by President Alvaro Uribe. In the past year, the ranks of its leadership have been depleted by illness and capture. Thousands of its soldiers have deserted, and in July the Colombian military rescued Ingrid Betancourt, the former presidential candidate, who had been Farc's most high-profile hostage. The sense that the tide is moving against the group is rising.

But we need to recognise there is only so much that can be done at the supply end of the drugs trade. Poor countries will always struggle to control traffickers. And even if Colombia succeeds, the cultivation of narcotics will most likely spread to other, less stable, parts of the world, perhaps Africa. It is no coincidence that chaotic Afghanistan is now the world's largest exporter of heroin.

It is up to us in the rich world to take a lead by staunching the demand for drugs through rehabilitation programmes and other radical measures. Mr Calderon's point is well made. The drugs trade is not just a responsibility for exporter countries. It is a matter for all of us.