His response, while swift, was not what British and US military trainers who have spent the past five years schooling the Iraqi security forces would have hoped for. He and 15 of his comrades took off their uniforms, kept their government-issued rifles and went over to the other side without a second thought.

Such turncoats are the thread that could unravel the British Army’s policy in southern Iraq. The military hoped that local forces would be able to combat extremists and allow the Army to withdraw gradually from the battle-scarred and untamed oil city that has fallen under the sway of Islamic fundamentalists, oil smugglers and petty tribal warlords. But if the British taught the police to shoot straight, they failed to instil a sense of unwavering loyalty to the State.