Iraqi soldiers hoisted the nation’s flag over the Basra palace compound on Monday after British troops withdrew from their last garrison in the city, leaving the country’s second biggest city largely in the hands in the hands of Iranian-backed Shiite militias.

British vehicles rumbled out of the gates of the sprawling Basra Palace compound after dark on Sunday and headed for the Basra’s international airport, about 12 miles away, where the last of Britain’s 5,500 soldiers are based.

British Prime Minister Gordon Brown said the move was planned for months and that British troops would be available to help Iraqi forces “in certain circumstances”. “This is essentially a move from where we were in a combat role in four provinces, and now we are moving over time to being in an overwatch role,” Brown told the British Broadcasting Corporation.

“We are able to give training... The purpose of this has been to hand the security over from the British army to the Iraqi security forces.”

In a report last June, the International Crisis Group, a Brussels-based think tank, said Basra residents and militiamen would consider the British departure “not as an orderly withdrawal” but as “an ignominious defeat”. “Today, the city is controlled by militias, seemingly more powerful and unconstrained than before,” the report said.

The report said Basra offered a “case study of Iraqs multiple and multiplying forms of violence” and a frightening picture of the country’s future if coalition forces leave without power-sharing agreements among Sunnis, Shiites and Kurds to guarantee peace.

A British military statement said the operation began at 10:00 pm on Sunday “with all British troops arriving at the airport by midday” Monday.

“There were no attacks on British forces. The formal handing-over of the Palaces will happen in the near future,” British spokesman Maj Matthew Bird said.