This is what the BBC says:
"The Shia militias will hope to upset these calculations so that they might claim credit for driving the British from the city and in Basra today, there is a definite sense that the end game has begun. "
The British Army wants to leave. They don't think they can do much any more. I don't know if they're right, but they probably know what they're talking about. I have to say that I think they'd probably be doing a better job if they were in Iran