The British Army's authority has never looked more fragile

The price from the British point of view - though probably there was no alternative to paying it - was to leave much authority in the hands of local political parties and militias, particularly those successful in the election in January. Since the beginning of the year the Shia militias, often now acting as part of the local police, have been consolidating their control.

They have assassinated their overt and covert opponents. They are eager to take over sources of income - such as rake-offs at the Basra oil refinery. In Basra earlier in the year, the police chief admitted that he had lost control of three-quarters of his 13,600 men to the religious parties.

A British aim from soon after the invasion in 2003 was to avoid alienating the local population and not to fall into the trap of over-reacting to any apparent provocation. What could happen if local people were provoked was savagely demonstrated in Maj al-Kabir, the marsh town just south of Amarah on the Tigris in the summer of 2003, when six British Royal Military Police were killed after they were besieged in the local police station until they ran out of ammunition.

On the whole, the British Army seems to have been more successful than the Americans in avoiding obvious cultural friction. Most important has probably been an unwillingness to open fire in all directions when a shot is fired at them. In Amarah, a peculiarly tough town that even Saddam Hussein found difficult to subdue, a British unit came under prolonged bombardment by mortars last year without responding. This is very different from Baghdad, where every Iraqi, both Sunni and Shia, has a story of a friend or relative killed by American troops.

Of course it is easier for foreign troops in Iraq in areas which are predominantly Shia. The uprising against the occupation forces has always been overwhelmingly led by Sunni forces. There are Sunni in Basra and other towns but they are a long way from their heartlands, where their support is strongest. But, at the same time, resistance cells have been able to operate in and around Basra with roadside bombs - although who exactly set up these resistance groups remains a mystery.

Ever since the invasion was first launched, both the American and the British military have tended to underestimate the gut dislike by Arab Iraqis - Shia as well as Sunni - of foreign occupation forces in their homeland. This may be stronger among the Sunni but Shia are often equally nationalistic. The difference is the Shia want to gain power first through elections. The Kurds are the only community within Iraq's borders genuinely enamoured of the American presence.

The British presence is also easier because there has never been the social breakdown in and around Basra - where the British forces have been concentrated - as there has been in Baghdad.

Kidnappings and robberies, which have so demoralised or driven into exile people in the Iraqi capital, are far less common in Basra.

The fragile understanding between the British army and local powers may well continue. But at some point the relationship between the two could break down and the cities and towns be engulfed by the same violence as is seen further north.