One in five of Britain's elite SAS troopers has been killed or seriously wounded in Iraq since 2003, according to special forces' insiders.

The Hereford-based regiment has suffered seven dead and at least 47 wounded from a total fighting strength of less than 300 in its four "sabre" squadrons. The casualties include 30 with critical wounds which have resulted in amputation of one or more limbs or life-threatening head injuries.

The loss rate is about twice the 10% average even for conventional infantry units which have taken part in the heaviest fighting in Afghanistan in the last year.

It also has a greater impact because of the experience and training needed to join the SAS and a growing shortage of qualified replacements.

Most sustained damage long after the initial invasion while part of a covert intelligence-gathering and counter-insurgency group known as Task Force 88.

The group is based in Baghdad but has an outstation at Balad, north of the Iraqi capital in the Sunni insurgent heartland.

An SAS communications expert was among 10 servicemen killed when an RAF Hercules was shot down by ground fire en route for the US special forces' base at Balad in January 2005.

The regiment has maintained a 60-strong detachment in Iraq since 2004 on a rolling, six-month deployment rota shared among its four fighting formations.

At least one of these sabre squadrons is always on standby in the UK in case of a terrorist incident or siege, while the others are on leave, training to deploy or involved in clandestine operations.

The SAS mounted one of the biggest raids in its 56-year history against a drug refinery in southern Afghanistan in November 2001 in Operation Trent.

Some 120 troopers staged a mass frontal assault, killing up to 60 drug traffickers and destroying large stocks of opium. Several troopers were wounded and the entire force had a near-miss from strafing US close-support pilots who mistook them for the enemy.

But it has since largely devolved responsibility for Afghan operations to its sister force, the Royal Marines' Special Boat Service.

It was SAS troopers who located Saddam Hussein's two sons, Uday and Qusay, in the city of Mosul in 2003. Both were killed when US commanders insisted on taking charge of such a high-profile capture operation.

They deployed missile-firing helicopters and 200 soldiers. Four US personnel were wounded.

The SAS had a 12-man snatch team on site and are still convinced they could have taken the targets alive.

Senior British officers are now concentrating on extracting a 400-strong UK special forces group from Iraq so they can be deployed to Afghanistan for a major offensive against the Taliban and drug traffickers next spring.

Inside Task Force 88, the UK contingent is known as Task Force Black. It operates from a building in Baghdad's Green Zone known as The Station House.