The announcement by Margaret Beckett that the allied handover to Iraqi forces would be complete within 18 months comes hard on the heels of Japan’s statement that its 600 non-combat troops will leave within the next few weeks. But overshadowing both hopeful signals has been the grim news yesterday that the two missing US soldiers have been found decapitated, their bodies showing signs of barbaric torture. They were apparently murdered on the orders of the new al-Qaeda leadership. At the same time a senior British commander has given warning that the situation in Basra is becoming worse and that a power struggle between Shia factions has led to a “worrying” amount of violence.

Taken together, these events underline the immense task facing the coalition in its attempt to ensure an orderly transfer of power and authority to the Government of Nouri al-Maliki. The insurgents are determined to make the exit of allied troops as bloody as possible and to challenge the Government before it is able to enforce a new crackdown. They have reverted to obscene carnage in an attempt to mock claims that the killing of Abu Musab al-Zarqawi had weakened al-Qaeda and that many among the terrorists were themselves disgusted with al-Zarqawi’s barbarism.

To its credit, the Iraqi Government has, nevertheless, kept its nerve. Hoshyar Zebari, the Foreign Minister, insisted in London yesterday, after talks with Mrs Beckett, that coalition forces would hand over security in the southern Maysan province, where about 170 British troops are stationed, as soon as Iraqi troops were ready. He has clearly understood that even among those allied nations committed to Iraq’s security and integrity, domestic political pressure is forcing the governments to look at the timetable and logistics for withdrawal.

Any withdrawal, however, must be managed with the care and caution that marked the announcement yesterday by Junichiro Koizumi, the Japanese Prime Minister. The Spanish alternative — a rash and sudden pull-out, dictated by domestic pressure — would be as disastrous as it would be irresponsible. Even the setting of a firm timetable might embolden the insurgency and increase the violence not only between Sunni and Shia but within Shia factions striving for political supremacy. The US, especially, needs to keep focused on the proposed gradual transition to Iraqi control and not allow any understandable emotional reaction to the grotesque murders to throw co-ordination with Mr al-Maliki’s Government into disarray.

As Mr Zebari said yesterday, foreign troops must not leave behind a security vacuum. The gradual handover of other provinces can only be achieved if the Baghdad Government is ruthless in confronting al-Qaeda and enforces whatever curfews and controls are needed to improve security. Poor governance has provided a fertile environment for the violence in Basra. British and US forces on the ground will inevitably struggle to help Iraqis if the elected Government in Baghdad does not take its responsibilities seriously.