Miles away from a functioning bank, opium acts as a form of credit in Afghanistan: the country which is the source of almost 90 per cent of the world's heroin.

Drug smugglers advance small farmers money against the following year's harvest and, acting as loan sharks, often double the money owed if the crop fails or is eradicated.

Eradication efforts in Badakhshan province, where opium cultivation dropped last year by 53 per cent, have led to a surge in reports of child marriage to level debts to drug dealers.

'Ten years ago before people started growing opium, you saw people selling their daughters, selling their children, and now it's happening again. People are desperate and are looking for husbands for girls as young as eight to make ends meet,' said Fazel Rahman, a trader in the Argu drugs bazaar, an hour's drive from Deh Magas.

'When the dealer asked for a daughter to marry to pay off the debt I didn't think to ask my family. I just said yes,' Abdul Satar said. When he went home and broke the news his eldest daughter became hysterical and threatened suicide, he said.

'It's not like the old days when you could just lead the girls by the nose like cattle into marriage,' he said. 'Now they have heard all about human rights on the radio and won't just quietly accept things.'

Now the old man has a dilemma on his hands. Neither of his daughters want marriage, but the drug dealer won't take no for an answer. 'I don't owe this man a daughter. I owe him money, but he won't wait,' he said.