Military planners are preparing to cut the number of British troops in southern Iraq early next year, possibly to about 3,000 in April or May.

The Ministry of Defence said yesterday that no political decisions had been taken about cutting the size of the force to below 5,000, and this figure is now expected to remain relatively constant for the rest of the year.

However, defence sources said that options were being studied that could lead to substantial cuts in spring, provided there were no security setbacks.

The next rotation of troops to Iraq, from the 4th Mechanised Brigade, is due to be completed by December 15.

Defence sources said that, under present thinking, the brigade’s full force of 5,000 soldiers, already training for Iraq, would still be sent to replace the current brigade, which is now based solely at Basra airport after yesterday’s withdrawal of 500 troops from Basra Palace.

However, for the following troop-rotation in April or May next year – replacing 4th Mechanised Brigade – it is expected that the numbers will fall significantly.

The sources explained that, by then, the Iraqi security forces would have had time to get used to being in charge of the whole of Basra province. Britain still retains responsibility for the province, despite the pullout from the city, but the MoD said that Iraqi troops would be ready to take over the whole area “in the autumn”.

One defence source said: “We will need to keep 5,000 troops in Basra province during the early stages of Iraqi control just in case there are problems and they need our help, but after a few months, it should be possible to start considering a reduced force – but not until early next year.”

The military planners will go to Iraq to work out where the cuts can best be made.

Gordon Brown, who is to make an announcement to the Commons next month about Britain’s future role in Iraq, said that despite the withdrawal from the city, troops would still be able to intervene in Basra in “certain circumstances”.

He told the BBC Radio 4Todayprogramme: “The numbers of troops are remaining roughly the same at this moment and we are staying to discharge our obligations to the Iraqi people and international community.”

Lieutenant-Colonel Patrick Sanders, the commanding officer of the 4th Battalion The Rifles battle group, said that the last three months in Basra Palace had been a “life-changing experience” during which six soldiers had been killed as the palace came under frequent attack by Shia militia forces.

Britain will continue to train the 17,250-strong Iraqi 10th Division in the south. Although there is now only one British base left, at the airport, troops are still located at the Shaibah logistics base south of Basra city, which was handed over to the Iraqis this year, and along the border with Iran in Maysan province.

Times Recommends

• Henning Mankell: ‘If Wallander was alive, I wouldn’t be a friend of his’
• Secret society's skull and crossbones for sale
• Nigerian leader vanishes after medical treatment