Britain concluded its naval training mission in Iraq on Sunday, more than eight years after it contributed the second largest contingent of troops to the US-led invasion that ousted Saddam Hussein.

Despite having pulled out the vast majority of its troops in mid-2009, Britain's Royal Navy has continued to train Iraqi personnel to defend their territorial waters and offshore oil installations.

"Their contribution was most appreciated and valuable," Foreign Minister Hoshyar Zebari told AFP.

"They have given many sacrifices to stabilise (Iraq) and they were the second-largest force of the coalition.

"Mistakes were made, not only by them, but by all of us," Zebari added, declining to give specific details.

"But that doesn't diminish their valuable contribution to training, capacity building and, recently, for the protection of our oil ports at the tip of the Gulf."

Iraqi government spokesman Ali al-Dabbagh said in a text message that the British naval training mission had 'finished' and, when asked to confirm that there were no more British soldiers or sailors left in Iraq, he replied: "Yes."

Some 46,000 British troops were deployed to Iraq in March and April 2003, at the height of combat operations that resulted in Saddam's overthrow and eventual execution for crimes against humanity.

In the aftermath of the invasion, the country was engulfed in a brutal sectarian war which peaked in 2006 and 2007. Tens of thousands of Iraqis died.

Violence has since declined, but attacks remain common.

A total of 179 British personnel have died in Iraq in the past eight years.

A small number of service personnel will remain at the British embassy in Baghdad.

"The actual UK maritime agreement comes to an end today but pretty much everyone was out Thursday and Friday," a British defence ministry spokesman said.

"The actual guys came out a couple of days ago."

He added: "There's a few staff left in the diplomatic corps but the deployment of military personnel has finished."

London formally ended military operations in Iraq in April 2009, and pulled out its forces in July that year, but has since been involved in the bilateral naval training mission.

That same year, then prime minister Gordon Brown opened an independent inquiry into Britain's role in the invasion and its aftermath. The inquiry is expected to issue a final report later this year.

The Royal Navy's role has involved training 1,800 Iraqi personnel on 50 different courses ranging from oil platform defence to handling small arms as part of efforts to secure Iraq's southern oil export terminals, through which the vast majority of its crude exports pass.

Around 90 per cent of Baghdad's government revenues come from oil sales.

British forces will continue to support NATO's officer training programme, while some Iraqi soldiers will attend the army's officer training college at Sandhurst.

Most of Britain's troops were based in the predominantly Shi'ite southern port city of Basra.

Basra, Iraq's third-largest city and a strategic oil hub, had been under British command since the 2003 invasion, but the province and its airport returned to Iraqi control in 2009.

The withdrawal comes 52 years after Britain's previous exit from Iraq, in May 1959, when the last soldiers left Habbaniyah air station near the western town of Fallujah, ending a presence that dated back to 1918.

It also comes with just months to go before a year-end deadline for the 45,000 US troops still stationed here to withdraw from Iraq under the terms of a bilateral security pact.