Speaking at the Royal Institute of International Affairs, Mr Browne said that he expected to withdraw a substantial number of the 7,200 British Armed Forces in southern Iraq by the end of next year.

The reduction will be possible when British soldiers hand over responsibility for Maysan and Basra, the last two provinces under their direct control. Maysan is due to be transferred in January and Basra in April. “If both these go to plan, we will be able to start drawing down our forces,” he said. “By the end of next year I expect the numbers of British Forces in Iraq to be significantly lower, by a matter of thousands.”

Whitehall officials expect the number to be halved but British Forces will remain at brigade strength with armour and air support at Basra airport and the Shaiba logistics base south of the city.

Yesterday’s announcement did little to satisfy demands at home and in Iraq for American and British forces to set a timetable for a complete withdrawal. “Des Browne will have to try much harder if he wants to satisfy calls for a detailed plan for withdrawal,” Nick Harvey, the Liberal Democrat defence spokesman, said. “Vague assurances are not enough.”

Italy, once a significant contributor with 3,000 troops in southern Iraq, said yesterday that the last of its forces would leave the country this week. Poland said that all its 900 soldiers would be home by the end of next year. Japan withdrew this year and many other states plan to follow suit.

Mr Browne insisted, however, that reducing the size of the British contingent in Iraq did not mean that Britain was withdrawing, and said that there was no timetable for a full pull out. “We need to be clear: the handover does not mean withdrawal,” he said.

British Forces will remain to back up the Iraqi police and Army and help to protect the vulnerable supply routes from Kuwait used by US forces to bring food, fuel and ammunition to their bases in central and northern Iraq.

For the first time Mr Browne also suggested that the British could embark on a new role that would last for five to ten years. This would be to bolster the Iraqi armed forces until they are capable of maintaining order at home and of defending the country’s borders.

“Our long-term relationship with Iraq will depend on the Iraqi Government’s position and on the circumstances,” he said. “I am not at this stage seeking to set out what the level of troop deployment will be in five or ten years’ time.”

One crucial factor shaping Iraq’s future could be the role of its powerful neighbours, Iran and Syria, who are blamed for stoking the violence by helping Iraqi insurgents and militants. The Iraq Study Group, an influential American review panel, is expected to recommend to President Bush next month that he open talks with Damascus and Tehran to help to stabilise the situation in Iraq.

Mr Browne said that Syria had recently “shown signs of constructive engagement” in Iraq by sending its Foreign Minister to Baghdad to announce the full restoration of diplomatic relations. He added, however, that Iran’s behaviour remained a cause of deep concern and he accused Tehran of backing groups attacking British Forces.

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