The conviction of Faryadi Zardad will prompt dancing on the streets of Kabul, an aid worker who saw his reign of terror at first hand has said.
Zardad controlled the road between Kabul and Pakistan
Guy Willoughby, director of anti-landmine group Halo Trust, described the Afghan warlord as a "nightmare" and "the nastiest of the very nastiest".
"People in Kabul will be delighted that the court case has gone like this."
Mr Willoughby, who gave evidence to the Old Bailey trial, recalled how Zardad's men had grabbed and abused civilians.
He told the BBC: "There have been good, not so good, bad, bad and very ugly warlords but he definitely took the biscuit. He was the worst when it came to torture.
"Many a time we were going through the check points and there would be civilian buses which had been pulled over by Zardad's men and there were people being pulled off and thrown into dungeons.
"He controlled the checkpoint on the only road between Kabul and Pakistan where, during the heaviest fighting in the 1990s, where hundreds of thousands of people were trying to leave Kabul, they had to go through Zardad's checkpoint, with all their family possessions.
"He was the nightmare scenario for people as they left Kabul, having to pass Zardad."
Another aid worker, Ed Strickland, who worked in the area controlled by Zardad, told the BBC the warlord's area of control was notorious.
"People always feared travelling down that road, especially people who had been in exile in Pakistan for some time who were fearful anyway coming back into Afghanistan, but to travel that particular section through Sarobi.
"I've had people sitting in the car next to me who were actually physically shaking and that's no exaggeration."
Joshua Rozenberg, legal editor of the Daily Telegraph and former BBC correspondent, said it was extremely unusual for UK courts to try cases where neither the perpetrators nor the victims were British.
Torture has been regarded as a "crime of universal jurisdiction" since a House of Lords ruling 1999 in the case of the former Chilean dictator Augusto Pinochet, he said.
"That means that crimes that took place in Afghanistan between 1991 and 1996 are within the jurisdiction of our courts.
"Afghanistan and the UK are both parties to the UN torture convention and are bound either to extradite or to prosecute."
As there was no request from the Afghan authorities, Britain decided to proceed with a prosecution, he added.
UK director of rights group Amnesty International Kate Allen said the prosecution was a major step forward in the fight against torture
"This case strengthens the legal principle that torture is an international crime and that there is no hiding place for torturers around the world."
Kevin Laue, a human rights lawyer with anti-torture organisation Redress, said he was pleased that the UK had followed the prosecution through.
"This sets a very important precedent in the sense that it sends a clear message to the perpetrators of torture who come and settle here or pass through.
"It shows that he or she is not immune to being prosecuted."
While he understood it was not easy to prosecute suspects who were just "passing through", Mr Laue said Redress would like to see more investigations and prosecutions of this kind.