Foreign Secretary David Miliband has defended the UK's continued military presence in Afghanistan, after eight soldiers were killed in 24 hours, BBC reported.
Some 184 service personnel have died there since 2001, more than the 179 killed in Iraq.
With Britain's role being called into question, Mr Miliband said UK forces were stopping Afghanistan becoming "a launch pad for attacks" by terrorists.
"This is about the future of Britain," he added.
Lt Col Nick Richardson told the BBC from Afghanistan it had been a "hard week" and that the risks had been higher recently because troops had been "taking the battle to the enemy".
"It's the only way to secure a future for Afghanistan and ultimately eliminate the risk posed to the international community that the Taliban and insurgents there bring," he said.
"We ask people to remember 9/11 and 7/7 and ask themselves whether they thought trying to prevent this from happening would be a worthwhile cause."
Fifteen soldiers have died in 10 days in southern Afghanistan as UK troops continue Operation Panchai Palang, or Panther's Claw, a major assault against the Taliban in Helmand ahead of next month's Afghan elections.
The deaths have brought the UK's role in the conflict under increased scrutiny.
British forces in southern Afghanistan been joined by about 4,000 US and 650 Afghan troops for the mission.
The Stop the War coalition has announced an emergency protest in London on Monday, calling for British troops to be withdrawn from Afghanistan in light of the heavy losses.
A group spokesman said: "The troop surge which was meant to pacify Helmand province has become a nightmare for the British army.
"This unwinnable war must stop now."
However, Mr Miliband told BBC Radio 4's Today programme troops were there to "ensure that Afghanistan can not again become an incubator for terrorism and a launching pad for attacks on us".
"This is about the future of Britain because we know that the borderlands of Afghanistan and Pakistan have been used to launch terrible attacks, not just on the US but on Britain as well," he added.
The mission would not be over until the 65,000-strong Afghan security forces had been increased to the 120,000 needed to defend the nation, he said.
Mr Miliband refuted claims by Conservative leader David Cameron that those fighting on the front line were not properly equipped - particularly with helicopters.