Britain announced Thursday that an 850-strong battle group from the crack Black Watch regiment would be posted outside Baghdad, where they would go under the "tactical control" of US Marine Corps commanders.

The Black Watch, along with the vast bulk of Britain's 8,500 troops in Iraq, are currently based around the southern city of Basra, which has seen relatively little violence in recent months.

This has been credited in part to decades of peacekeeping expertise British forces gained in places such as Northern Ireland, Bosnia and Kosovo, with some commentators contrasting this with what they see as more gung-ho US methods.

The redeployment will free up US troops for an expected assault on insurgents in the violence-plagued western city of Fallujah.

Some opponents of Prime Minister Tony Blair -- and even rebel members of his Labour Party -- have expressed concern at the idea if British troops coming under US command.

However Britain's most senior military officer, Chief of the Defence Staff General Sir Michael Walker, insisted Friday that the move was nothing more than "business as usual".

"This allows the local commander of the unit to which they are being attached to have the authority to co-ordinate the various units under his command," he told BBC radio.

"But he has no authority to give them orders that would be against the sort of doctrine and training we undertake."

Fears that British soldiers might be forced to adopt aggressive US tactics was based on nothing more than "a lack of knowledge", said respected independent defence analyst Paul Beaver.

"We are talking about NATO nations," he told AFP.

"There's basically no administrative problem in doing this. We've been doing it in Bosnia and Kosovo and Afghanistan for more than a decade."

British soldiers would still operate under their own rules of engagement, which were immovable, he added.

"The military cultures are different between every nation. But that doesn't stop the operation from going ahead, we've worked with the Americans consistently for 60 years.

"Rules of engagement are like military orders, they are binding on the soldier," Beaver said.

According to Thomas Withington from the Centre for Defence Studies at King's College London, multinational command -- known in military parlance as "jointery" -- was a vital component of modern warfare.

The Black Watch, if based in a US area, had to be under US control for reasons of "simple, sheer practicality", he said, allowing them to call in US air strikes and minimising the risk of so-called friendly fire incidents.

However there were likely to be some differences in culture between the British troops and the forces under whose command they will comes, the 24 Marine Expeditionary Unit.

As well as being heavily armed with tanks and attack helicopters, the Marines were an elite attack force, Withington said.

"They are extremely well-trained, extremely aggressive. They are designed to do some pretty unpleasant stuff," he said.

"The way that they behave on the ground sometime reflects that... With the Brits, things are very different."

A "key difference" was US forces' relative lack of peacekeeping experience, he said, while stressing that any tensions were likely to amount to little more than "a bit of eyebrow raising here and there about methods".

"If there is any tension, or mutual scepticism it will not come to the fore, it will be ironed out," Withington said.

"It's there, and there are some questions about how the Americans do fight, but in the heat of battle both forces are professional enough to make it work."

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