Although officials have been reluctant to give out detailed information so soon after the raid, the foreign secretary did say that it took place early today and that "mercifully, no shots were fired".

The Ministry of Defence also confirmed that British troops had played a "prominent role" in the rescue operation, which took place in western Baghdad.

John Reid, the defence secretary, said the operation, "spearheaded by British troops" had been "several weeks" in the planning.

Both departments stressed that it was a multinational team that secured the release of the peace activists, and that it included Iraqi civilians.

It is a moot point as to whether Iraqis may be more willing to work with the coalition despite or because of the growing sectarian violence. But it is nevertheless significant, since without good information about where the hostages are being held, it is impossible to mount a rescue.

At a US military briefing in Baghdad, General Rick Lynch said two people were arrested yesterday who provided the location of the hostages. He said the information was received around 8am today (0500 GMT) and the operation mounted.

The three hostages were found bound and together in the same building and no kidnappers were there at the time. "The key point is that the operation was intelligence-led and the information was provided by a detainee," he said.

Defence experts said it was likely that Iraqi and American forces had played an important role in pinpointing the strike location before handing over to the SAS to carry out the raid. The British special forces are understood to have a permanent base to the north of Baghdad and have been on constant standby.

"The hardest part of a mission is gathering the information and making sure you have the right place and the right person," said Robin Horsfall, a former SAS soldier who took part in the storming of the Iranian embassy in London in 1980.

"The most dangerous part is going in to get them but that is not the hardest bit. Clearly they got very accurate information and did a good job," he told Sky News.

"From the limited information that we have it looks like they made an assault on a building. They have made a clean and clinical operation. The fact that we have live hostages and it appears there have been no casualties is testament to that.

Andy McNab, who served with the SAS in the first Iraq war, said it appeared today's operation had been "flawless".

"The key to these operations is the information. Once a target has been identified, the commander would have started to form a plan and could well have sent in covert operators to check out the area. You need to know the detail, like, is the front door made of wood or metal, so you can work out the equipment needed to get in."

He told Sky News that although it was a multi-national operation, there would not have been British forces going in on one floor and Americans on another.

He said they would have been allocated different roles within the operation with the Iraqis likely to have been guarding an outer cordon to prevent people entering or kidnappers escaping.

A military operation to free captives is a first for the release of hostages in Iraq. Other high profile releases after a prolonged captivity - such as those of the Italian aid workers Simona Torretta and Simona Pari - have often come amid claims that ransom payments were made.

But the disastrous raids by Russian security services in Moscow in 2002 and in Beslan in 2004, when scores of hostages were killed, show the inherent risks of mounting a special forces operation.

Mr Horsfall said the SAS had been able to maintain its high standards through taking the best personnel from various branches of the armed services.

"Its compact size means it has been able to keep very high standards," Mr Horsfall said.

"You have to have served for at least three years before you can volunteer. Only around 10% of those then pass the training. Their average age is probably 27-31. They have a very high fitness level but also are intelligent. They may have foreign languages or experience with medicines. They are at the very peak of professionalism."

The SAS, or Special Air Services regiment, was formed during the second world war. Early missions involved raiding German camps in Egypt and parachuting into occupied France to destroy bridges and prevent Nazi forces redeploying to counter the Allied landings.

Its most famous mission was probably the storming of the Iranian embassy in London in 1980 when, in front of the world's press, troopers abseiled into the building and rescued nearly two dozen hostages.