Greeks bomb Scotland Yard?
If you imagine a situation in which the Greek army acting as peacekeepers in the UK allied with the scottish dominationed national government of the UK blew up Scotland Yard you would part understand how risky the attack on the Basra police station is.
I don't like second guessing military tactics as you need to know what the situation is on the ground in detail. However, it appears that the UK forces in Basra are now working against the local council.
Segmented societies tend to divide into factions. Tribes or clans can switch from faction to faction. However, most feudal disputes are based upon feuds or vendettas which arise from a desire for revenge. There are a number of good books on the motivations for Suicide Missions which basically show that revenge rather than religion is the key motivator.
I am concerned that this particular action by the UK forces may be seen in retrospect as something increasing the level of disorder in the south. I may be wrong. I am writing from Birmingham rather than on the ground in Iraq. It looks like something that will up the ante, however.