When Nouri al-Maliki launched his surprise attack against the main Shia militia in Basra, the operation appeared to be a disastrous miscalculation pitting inexperienced Iraqi soldiers against well-armed and battle-hardened street-fighters of the Mahdi Army.

Scores of soldiers defected from their ranks. Iraqi armoured vehicles were ambushed and destroyed by jubilant militiamen. An American general and several hundred US paratroopers had to race down to Iraq’s southern capital to rescue the operation with British forces offering air cover and logistical help.

The Iraqi Prime Minister, accused like his predecessor of indecision and a failure to tackle the pressing security problems facing his country, had taken personal control of the operation. It emerged that he ordered the assault weeks ahead of a more carefully planned offensive in conjunction with American and British advisers. Some predicted that the military blunder signalled the end of his unimpressive period in office.

One month on and Iraq’s leader can justifiably claim to have scored a stunning victory, probably the first of its kind by the post-Saddam Iraqi army. The most notorious areas of Basra are now under government control, the Mahdi Army of Moqtadr al-Sadr has been roundly defeated and the long suffering people of Basra are celebrating freedoms they did not enjoy during the four years of British military rule in the city.

So how did a military novice, using untested troops, succeed where thousands of British forces had failed?

The hint came at the weekend from the unlikely figure of Hassan Kazemi Qumi, the Iranian ambassador to Baghdad, whose country has in the past armed, funded and trained elements of the Mahdi Army.

“The idea of the government in Basra was to fight outlaws,” said the envoy. “This was the right of the government and the responsibility of the government. And in my opinion the government was able to achieve a positive result in Basra.” The Iranian embassy in Baghdad is not given to making any public statements, certainly not comments that support operations backed by the Great Satan, as America is called in Iran. But in the arcane world of Shia politics his comments made perfect sense.

While British forces were in Basra city, it was in Tehran’s interests to drive them out by backing various militias that would help consolidate Iran’s control over Iraq’s second city, the country’s only access to the sea and a region containing its largest oil reserves.

But once the British withdrew from the city centre to Basra airport last summer, the situation changed. Suddenly it was Moqtadr al-Sadr and his rag-tag fighters who were the dominant force in the Basra region. The Iranian backed Badr Organisation, which is well represented in Iraq’s police and military, was sidelined. There were real fears that the Sadrists could consolidate their gains on the ground in local elections planned for October and eclipse the Islamic Supreme Council of Iraq, Badr’s political wing.

For once the interests of America, Britain, Iran and the Iraqi government coincided with disastrous results for Mr al-Sadr and his fighters. Isolated and abandoned they fled, were captured or killed from what were once their impregnable fiefdoms in Basra. Mr al-Sadr was left to lick his wounds and complain that the Government had forgotten that they were all “brothers”.

The victory demonstrated what can happen in even the most lawless regions of Iraq when the main external forces, in this case America and Iran, act with common purpose.

Unfortunately, there is little evidence that the Basra example will be repeated any time soon. In Baghdad, US forces are currently engaged in an identical battle against Mahdi Army irregulars concentrated in their Sadr City stronghold. In response to US air strikes, the militia is firing Iranian-made rockets and mortars into the Green Zone, the heavily fortified area containing the US and British embassies.

The combatants may be the same as those fighting in Basra, but the political circumstances are completely different. In Baghdad it seems Iran wants the Mahdi Army to continue to have a piece of the Iraqi capital and a stake in the politics of the city.

The Iranian ambassador condemned America’s use of force in Baghdad and gave warning that it would lead to further bloodshed and more destruction. For now at least, his predictions have come true.

Times Recommends

• Karadzic found freedom in the Madhouse
• Bears kill guards at Russian mine
• Hotel is a monument to new North Korea