Defence Secretary John Reid told the House of Commons that the changes involve having 7 Armoured Brigade take over from 12 Mechanised Brigade.

"The total number of troops in Iraq following the deployment of 7 Armoured Brigade will be around 8,000," Reid told the first session of the House of Commons since it returned from its 80-day summer recess.

"This is about 500 fewer than at present, reflecting the closure of two small bases in Basra, the transfer of some training tasks to the Iraqi security forces and structural differences between the two brigades," Reid said.

"These are relatively minor adjustments, however, and will not affect the activities being carried out by the United Kingdom forces," he said.

Reid has long said he hopes to begin the process of withdrawing British troops from Iraq within the next year as Iraqi security forces become better trained.

However, he also repeated Britain's determination to keep troops in Iraq as long as the government in Baghdad needs the US-led coalition forces, which invaded Iraq in March 2003 to overthrow Saddam Hussein.

Britain would not "abandon Iraq before it is ready to stand on its own two feet," Reid said.

He said British forces would remain for "as long as we are needed ... and no longer," but again warned of further "obstacles" ahead as insurgents oppose moves towards democracy.

"The biggest obstacle to our leaving Iraq is now the actions of the terrorists themselves. Terrorist activity only delays our leaving Iraq."

Reid faced questions about the infiltration of the coalition-trained police in Basra after British troops rescued two special forces soldiers who were detained by the police and then handed over to a Shiite Muslim militia.

"In any theatre of combat in the world where there are competing factions at war, there is always the problem about split loyalties," Reid said.

"The question is not whether those split loyalties are there but whether we can diminish them by human rights training and training the police to be as objective as possible," he added.

"There are certain elements within the police service within Iraq about whom we ought to be worried. But I would not want you to believe this is a majority or anything like it," he said.

The main opposition Conservative Party's defence spokesman Michael Ancram told Reid that "for all your brave words, the situation today in Iraq is grim" as the insurgency against the coalition and the government it supports raged on.

And though the troops had to see the job done, Ancram said, the mission for British troops to stay in Iraq could not be open-ended.

Since the US-led March 2003 invasion of the country, 95 British military personnel have died as a result of combat, accident or natural causes.

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