A bit more detail, from a UK Times reporter who used to be Mil Int...
http://www.timesonline.co.uk/printFriendly/0,,1-523-1796692-523,00.html
"THE BUILD-UP TO THE CRISIS
On Monday two SAS men in Arab clothes and an unmarked car clashed with local Iraqi police in Basra sparking a riot and political crisis. This is how they came to be there
In July three British soldiers were killed when a bomb struck their patrol vehicle at Amarah close to the Iranian border
Forensic examination of the device revealed it was a sophisticated bomb designed to penetrate the armoured Land Rover from below. Experts identified it as similar to bombs supplied by Iran to Hezbollah, the militant Islamic group
Intelligence from MI6 and GCHQ also revealed that Iranian Revolutionary Guards were on the ground in Basra posing as pilgrims on the way to Iraq's holy shrines and liaising with the militias
Military commanders decided to send the SAS into Basra to track the routes along which insurgents and bombs were being smuggled in from Iran. Two dozen SAS soldiers were dispatched from "the Station House" in Baghdad to Basra
The SAS teams conducted an overall review of the area to decide where to focus covert observation posts and close recce patrols. All SAS troopers in the field were in civilian dress, operating undercover
Each patrol was briefed in detail. At a remote part of their base they rehearsed "actions on", the precise responses to take in any likely circumstance, including contact with civilian police. They double-checked all equipment, including communications gear and weapons
SAS patrols both in car and on foot then began a bid to track down and trap the suspected arms smugglers
On Monday last week, one of these two-man teams left their base by car - a battered Nissan - disguised as locals to gather intelligence and resupply another team
The car was stopped by a police officer who was shot in leg as the SAS team tried to avoid capture
The two SAS men sped off but were pursued by Iraqi police. After a chase in which a passerby was killed by a stray bullet, they were captured
