As the Royal Navy concluded their training mission last week, it marked the official end of the British military operations in Iraq. The task of training Iraq’s nascent navy is crucial due to the strategic importance of the southern oil ports and the 90 percent of Iraqi revenues that comes from selling crude.

When the British ended their combat mission in May 2009, a morbid roll call was read out during the ceremony to hand over control to the US army, honouring the fallen soldiers of the coalition forces in the south. The names included 179 British personnel who lost their lives during the conflict.

Britain’s nemesis in Iraq was neither al-Qaeda and the foreign fighters that poured into the country through the porous desert frontiers in the west, nor the Ba’athist insurgents who desperately tried to destabilise the political process. Their deadliest enemy in Iraq was the Iran-backed Mehdi Army, the Shia militia that is currently ‘on hold' but still threatens the peace in Iraq today.

Britain’s worst mistake in Iraq remains their “accommodation” of this unpredictable and violent militia. British intelligence struck a secret deal with the Mehdi Army and its leader Muqtada al Sadr several years ago, the terms of which meant the British would withdraw from the city of Basra to their base on the outskirts in return for not being targeted. Defence Secretary Des Browne was the only person who could permit soldiers to return to the city.

The deal proved to be a disaster because the militias were given the space they wanted to terrorise locals and turn Basra into a lawless city. Defence officials denied that the agreement meant the British could not quickly provide support for the offensive campaign in March 2008 when the Iraqi premier decided to regain control over Basra. However, the damage had already been done and Britain’s reputation in Iraq took a severe blow.

Sadr’s militia were not the only bandits in Basra, and several other local and foreign-backed militias also added to the toxic mix of criminal gangs, but the Mehdi Army remained the most powerful of these.

The successful Iraqi-led 'Charge of the Knights' operation routed the militias whilst the British commander, Major-General Barney White-Spunner, was away on a skiing holiday. When his deputy arrived at the presidential palace in Basra to meet Maliki, he was ordered to wait outside. The message was clear: the secret deal with the Mehdi Army had been both counterproductive and unforgivable, straining the relationship between the British army and the Iraqi government.

The impression that the British left was one of incompetence and bad strategy. The Americans came to Iraq and took control of some of the most dangerous areas of the country, but eventually managed to bring about relative stability. The British came to Iraq and took control of one of the safest provinces in the country, but through mismanagement turned it into one of the most dangerous.

America also struck a deal with insurgents in Iraq, but in their case they turned erstwhile enemies into useful allies that turned against al-Qaeda, whereas the British deal only turned Iraqi against Iraqi and no benefit, short-term or long-term, came of it.

Basra residents were so glad to see uniformed Iraqi troops back on their streets – as opposed to the rag-tag militias – they rewarded Maliki in the January 2009 provincial elections with around 240,000 votes and the PM’s bloc won over half of the seats in the governorate. In contrast, Sadr barely won 32,000 votes and managed to control only 2 seats out of a total of 35. The message again was clear: the people would reward stability and punish criminality. It was no coincidence that after Maliki defeated the “outlaws” in Basra he named his electoral bloc “State of Law”

There were several episodes of sickening abuse carried out by British soldiers in Iraq but whilst in many of these cases the responsibility lay with the individual acts of a few – and condemned by the British authorities – the handing over of Basra to criminal elements could only have happened with the acknowledgment, and blessing, of Whitehall.

As it turned out, Maliki himself later made a separate deal with the Sadrist movement in a bid to stay in power. Sadr’s consent to the power-sharing government is key to its survival but may also be the reason for its failure in the future. As with the British deal two and a half years earlier, it remains to be seen whether this “accommodation” will have any long-term positive effect on the stability of Iraq.

Whilst the British did play a crucial role in overthrowing Saddam in April 2003, and whilst they did provide valuable training for Iraq’s security forces, they also made horrendous mistakes along the way that hindered Iraq’s political progress. The damage they caused may never be quantifiable because along with lives and physical destruction, Iraq also lost valuable income due to the smuggling of oil that was only made possible after allowing the criminal gangs to operate with impunity in Basra.

This summer is going to be extremely important politically for Iraq both because the peoples’ patience will be tested in the scorching heat with only a few hours of electricity a day, and also because tensions are already rising about the possible presence of American forces beyond 2011. There have already been public disagreements between key government officials and now everyone is hoping the spat will not be the reason for another round of violence and terror.

For now though, Britain is glad to have its troops come home and Iraq is glad to see them go. Many had hoped that Britain, whose history in Iraq predates the creation of the state itself, would have dealt with the post-2003 situation better than the US, but unfortunately, that has not been the case.