It is time for Britain to withdraw from southern Iraq, whatever happens in the rest of Iraq and whatever the US does. The British presence in southern Iraq could be regarded as a success story because there has been relatively little violence and local institutions have been established. But since the September capture by local authorities of two British soldiers clad in "Lawrence of Arabia" disguise and the subsequent storming of the prison where they were held, the tide has turned. British troops face the real possibility of being embroiled in a dangerous counter-insurgency war which they cannot win and which could overturn the real achievements the British can claim up to now.

Success is partly due to local consent - occupying the mainly Shia areas of southern Iraq was always going to be easier than some other parts of the country. But it is also due to British methods of peacekeeping, drawn from colonial experience and Northern Ireland, as well as Bosnia and Kosovo. The Americans have acted as occupiers rather than peacekeepers and their troops tend to focus on force protection and "search and destroy" missions. Indeed, the areas outside their safe zones are often called "Indian country", as was the case in Vietnam. As it is often difficult to distinguish insurgents from civilians, many innocent people get killed or detained and this deepens the rift between those - generally the elite - in protected zones who support the occupation and those who do not. This growing social polarisation risks being transformed into sectarian civil war because it is mainly Sunni areas that are targeted by US troops.