Plans to reduce British troop numbers in Iraq to 2,500 this spring have been abandoned on the recommendation of military commanders, UK officials say.
Gordon Brown, prime minister, announced in October that from spring Britain would seek to cut the force to 2,500, but added the proviso that the final decision would be "guided as always by the advice of our military commanders". An announcement is expected from Mr Brown on Monday or Tuesday, officials say.
There are about 4,100 British troops in Iraq, with a further 500 personnel providing logistics and support from neighbouring Kuwait.
Senior officers have now recommended that reducing numbers sharply would leave the force unable to protect itself adequately.
Officials said the recommendation was made before the upsurge in violence this week in the southern city of Basra as Iraqi government forces seek to disarm Shia groups.
Britain withdrew from Basra city in September and its forces are essentially confined to Basra airport.
There they continue the training of Iraqi government troops and say they are ready to provide combat troops in support of the Iraqi government if called upon.
The Ministry of Defence said on Friday that there had been no such request from the Iraqi government to help with the latest operation.
UK support had been limited to providing air surveillance for Iraqi government troops, but no UK munitions had been dropped to back up the government's operations.
The shift on cutting troop numbers raises questions about whether the UK will be able to lower troop levels in Iraq much below 4,000 unless it pulls out completely, which is unlikely before next year at the earliest.