The third and final part of Angus Macqueen's exploration of the failure of present drugs polices takes the viewer to the frontline. Birth of a Narco-State shows how the war on drugs is actually fuelling the long-term civil war in Afghanistan, possibly creating what he calls a 'Narco-Theocracy': a toxic mixture of drugs money and religious extremism.

Meanwhile, western demand for heroin generates huge profits that finances both sides in the civil war, corrupting the very government that British soldiers are fighting to protect.

This film gets under the skin of the drug trade in Afghanistan, from the deserts of the Afghanistan-Iran border to the smuggling centre of Herat and the courts in Kabul, engaging with those working to establish some sort of order in the face of overwhelming odds; all the time questioning whether it is our drug laws or our drug demand that is causing the problems in the first place.

Macqueen meets General Aminullah - former head of security at Kabul International Airport - who was sacked after exposing widespread corruption and then placed under investigation himself. We see shocking footage he took of a young, female Afghan burqa-clad drug smuggler demonstrating brazen disregard for the law, who then got off scot-free. Rarely has such an open example of what 'corruption' means been caught on camera.

Filming in the newly-opened - US and UK-financed - drugs courts, it becomes clear that many of the traffickers who are arrested are still 'small fish'. The big players always seem to get off; even the judges admit that they are too well-connected, often high up in the government, to the very people the British troops are fighting for and dying to protect. Afghanistan's president himself, Hamid Karzai, pardoned five convicted drug traffickers connected to his election campaign.

Allied policy to the drugs issue has been in confusion since the invasion of 2001: our troops have been told in some years to eradicate all poppies, and in others to leave them so as to win hearts and minds of the peasants. Sometimes different policies are carried out in different areas.

And all the time around 60 to 70% of the Taliban's funding comes from the heroin trade. The profits are staggering, with 10 kilos of opium - valued at around £400 in Afghanistan - making one kilo of heroin worth £40,000 by the time it reaches Europe.