The Afghan police are "undisciplined, badly trained and rather too keen to use violence to achieve their aims, according to a journalist who has spent time with them.

Nadene Ghouri, who has worked in Afghanistan for the past few years, told the programme that corruption in the force was "endemic", with those wishing to join paying for their jobs. This, she added, had created a police force "that ordinary Afghans simply can't trust", which had been implicated in in kidnapping, robbery and murders.

She said that problems with the police force date back to the years after the fall of the Taliban, when the emphasis was on equipping and training the Afghan army, something she called a "big strategic mistake". She added that there is increasing evidence to suggest that the Afghan police have been infiltrated by the Taliban.

Ms Ghouri's comments come in the wake of the deaths five British troops who were killed by an Afghan police officer they were training.