The soldiers were all killed as a result of gunshot wounds sustained in an attack in the Nad e-Ali district of Helmand province during the afternoon of 3 November 2009.
The attack is subject to investigation.
Lieutenant Colonel David Wakefield, spokesman for Task Force Helmand, said:
"It is with the deepest sadness I must inform you that five British soldiers were shot and killed yesterday in Nad e-Ali district. Five British soldiers, five of our own, shot down in the course of their duty. They will not be forgotten."
Defence Secretary Bob Ainsworth said:
"I was extremely saddened to hear of the deaths of these courageous soldiers. My very deepest condolences go out to their families, friends and colleagues as they come to terms with the loss of these outstanding men.
"It continues to be a difficult year in Afghanistan for our brave people who are operating within the most challenging area of the country. We owe it to them to show the resolve that they exhibit every day in building security and stability in Afghanistan and protecting the UK from the threat of terrorism."
The soldiers' next of kin have been informed and a period of grace will be observed before further details are released.