They were involved in training police as part of Britain’s mission to help Kabul to set up its own security forces.

Forensics experts are trying to establish whether their vehicle hit a landmine or was blasted by a roadside bomb. They died a month after another SAS reservist, James Thompson, 27, from Whitley Bay, was killed by an explosion.

Gordon Brown expressed his “deepest condolences” to the families. He said: “Our troops are the best in the world and fighting for the noblest of causes.” 

Tory leader David Cameron said: “Let us be absolutely united in saying that their fight is our fight. This is a fight against terrorism and extremism, not just in Afghanistan, that affects the safety of our streets and our way of life, too.” An indication of the fighting’s ferocity was revealed by figures showing that between December last year and last month, troops fired two million rounds. In March alone 920,000 rounds were fired.

This underlines claims that British troops are in a campaign of an intensity not seen since the Korean war more than 50 years ago.

The Intelligence officer was the first woman victim in Afghanistan but the seventh since forces were deployed to the Middle East as part of the war on terror. 

Though women are not allowed to join infantry units, they serve in a variety of other roles. One of two women killed in Iraq by a roadside bomb in April last year included Second Lieutenant Joanna Dyer, 24, of the Intelligence Corps, who was a Sandhurst friend of Prince William’s. The presence of the SAS reservists also shows the pressure under which our Special Forces are working, with Britain fighting on two fronts for more than five years.

Defence Secretary Des Browne said: “The last 10 days have been extraordinarily difficult for troops, for the families and for those who support them. We have now lost nine soldiers in 10 days and every single one of those losses is a tragedy. I cannot imagine the terrible grief they are going through. 

“But the Taliban are losing in Afghanistan. I know it may not appear like that at the moment, but we’re enjoying a degree of success.”

In recent weeks, British commanders have claimed that the fight against the insurgents was at a “tipping point”. Brigadier Mark Carleton-Smith,  commander of British forces, said: “The Taliban are much weaker. The tide is clearly ebbing, not flowing, for them. Their chain of command is disrupted and they are short of weapons.”

But unable to win all-out battles, they have turned to terrorist tactics including planting improvised roadside bombs.

Tory MP and former infantry officer Patrick Mercer said troops needed more helicopters. “If you have off-route mines, roadside bombs, why don’t we have the helicopters that are available?” he asked. 

Meanwhile, British paratroopers were still last night helping to track down some of the 400 Taliban prisoners who escaped from Kandahar prison last weekend after insurgents blew its main door off.