In June 2004, in a brief ceremony in the green zone of Baghdad, the US-led Coalition Provision Authority handed sovereignty of Iraq back to Iraqis. Since then the official position of both the US and British governments has been that their forces would leave when asked to by the sovereign Iraqi Government. In his interview in today's Times Iraq's Prime Minister has not quite issued a formal eviction order, but he has come close (see page 30).

Asked how important British troops were for security in the south of the country, Nouri al-Maliki said bluntly that at their current strength of 4,100 they were “definitely ... no longer necessary”. His remarks were intended partly as a show of independence for domestic consumption. They also left him room for flexibility over the continued deployment of British “advisers”, which in turn leaves Gordon Brown able to argue that by promising a “fundamental change of mission” by next year he has already agreed in principle to everything Iraq is demanding.

But there is no mistaking Mr al-Maliki's seriousness. He said of British Forces: “We thank them ... but I think that their stay is not necessary for maintaining security and control.” He gave repeated warnings that if the legal basis for Britain's military presence in Iraq is not renewed before its scheduled expiry date at the end of the year, British troops would have to leave forthwith. And he emphasised that the tasks he envisages for British military trainers beyond that date will not warrant a deployment on anything like the current scale.

How should Britain respond? The question is not made easier to answer by Mr al-Maliki's strongly worded criticisms of Britain's record in Basra, never mind his call for a withdrawal. He said that far from helping to bring security to Basra, British “military doctrine” may actually have delayed it; that the deal British Forces struck with the so-called al-Mahdi Army to enable them to withdraw from the city last year without casualties was a “disaster”, and that the withdrawal itself was premature.

The Ministry of Defence - and only the Ministry of Defence - continues to deny any such deal was agreed. In reality, the “accommodation” reached with Basra's Shia militias fatally mistook a murderous insurgency for mere criminal gangs. It dismayed both US and Iraqi commanders when they learnt of it and did serious long-term damage to the British Forces' reputation in Baghdad as well as southern Iraq.

Iraq's Prime Minister appears to have decided that, at a critical juncture, British Forces put their own security ahead of Basra's. Historians may agree. But it would be a shameful waste of blood and treasure to decide because of this that Britain's military mission in Iraq was suddenly over.

Iraq's 14th division is simply not ready to guarantee the city's security on its own. It still needs the British training and support that has brought it to its current strength, and Britain will continue to need a logistics base in southern Iraq in order to provide it.

The work of British Special Forces in central Iraq is even more significant, if less well known. As General David Petraeus has attested, the SAS has proved a crucial partner for the US Delta Force in its astonishingly successful bid to drive al-Qaeda from Baghdad.

Mr al-Maliki is not, in practice, demanding a precipitate British pullout. But Britain must heed his call for a swift resumption of talks to produce a new status of forces agreement that would define clearly how many British Forces are needed in Iraq, and what they should be doing. In these talks, only one thing matters, and it is not British honour or Iraqi self-esteem. It is Iraq's security.