The heaviest officers stand on top of the wooden roller and repeatedly ride it down the back of the calves of their agonised victim. Crucially, the torture leaves no scars.
More than 100 countries have now ratified the United Nations Convention Against Torture, yet secret police forces around the world are developing new methods of tormenting their captives which rival the barbarism of Medieval dungeons.
Algerian torturers favour "Le Chiffon", a thin wet cloth soaked in excrement, which is bound around the mouth and nostrils of the victim. The infamous Iraqi secret police, the Amn-ei-Kas, refer affectionately to their electrodes as "the earrings", while the Sri Lankan authorities like to suspend victims upside down with their heads in a plastic bag containing petrol.
We know this because some of the survivors have escaped to reach the doors of the Medical Foundation for the Care of Victims of Torture, an anonymous green building in a North London side street, which has become an internationally-renowned sanctuary for victims of serious human rights abuses.
It was the Foundation which provided affidavits from clients who had suffered at the hands of the regime of the former Chilean dictator General Augusto Pinochet, evidence which helped sway the Law Lords to rule that a former head of state had no immunity from prosecution for human rights crimes.
For Helen Bamber, the Foundation's phenomenal 73-year-old director, the time has come for increased diplomatic pressure to be applied by the international community against those countries which use torture.
She said: "I would like to see torture treated as a disease which we wish to eliminate as much as we want to eradicate cancer. Torture not only destroys individuals but their families and communities as well." The survivors who reach the Foundation are given a range of treatment from a team of doctors, psychologists, counsellors and physiotherapists who have developed a unique understanding of the long-term physical and mental effects of torture.
Unfortunately, when the refugees arrive in Britain, they invariably experience a reception which is less than welcoming. Instead of medication, they find themselves once again under interrogation from immigration officers whose sense of compassion has been undermined by the pressures of illegal economic migration. For Alex Sklan, the Foundation's director of clinical services, urgent action is needed to counteract the "culture of disbelief" which surrounds the interviews of torture victims as they try and claim in Britain.
He said: "After what they have experienced, it is quite shattering for them to be placed under cross-examination by someone who does not believe them."
During the past decade, the international traffic in refugees has been transformed by the resurgence of ethnic cleansing. Organisations like the Foundation, whose clientele had predominantly been tortured political activists, were faced with an influx of people seeking sanctuary from state racism, culminating in the arrival of Roma refugees from the Slovak Republic and ethnic Albanians from Kosovo.
Now the forthcoming Immigration and Asylum Bill will contain drastic measures to reduce the attraction of Britain as a destination for refugees. In future, asylum-seekers are to be accommodated away from London, in towns where torture victims will be unable to receive specialist medical help and are to be given vouchers instead of benefits.
The office of Sheila Melzak, the Foundation's co-ordinator of Child and Adolescent Psychotherapy, is plastered with the drawings of youngsters who have reached this country frightened and alone.
Some of the pictures - showing stowaways, huddled figures or bare and leafless trees - give an illustration of the troubled minds of the young artists. Others are depictions of the garish logos and brand names of trainers and clothes beloved by British youngsters but beyond the means of young refugees.
Ms Melzak said one of her young charges was a 17-year-old Tutsi boy who had arrived home from tending cattle one day to find his father butchered outside their rural Rwandan home.
Having fled to London, he now lives in a hostel for single adults where many residents have serious drink and drug problems.
Ms Melzak said: "These kids are very isolated and they don't get enough support. They are often seen as dangerous young men rather than vulnerable kids who have had their adolescence taken away from them."
Women torture victims also present special problems. Gill Hinshelwood, a doctor and psychoanalyst, said women refugees were often rape victims who were outcasts from their society. "They cannot even seek help from their own community in this country because they think people will know they have been raped," she said.
Most refugees arriving at the Foundation are looking for support from people who sympathise with the trauma they have suffered. Case worker Erol Yesilyurt can relate to their plight, having himself fled Turkey, where he was subjected by police to the ancient Ottoman torture of Falaka, where the soles of the feet are repeatedly beaten.
"I think it is important for the clients to see that there are good examples. I am a role model for them, Britain has been good to me," he said. "But when I compare my experience with those of genuine refugees who have been refused asylum, I have mixed feelings. I was able to re-establish myself and become productive.
Why weren't these people, who were just as deserving given the same chance?"
Donations to The Medical Foundation for the Care of Victims of Torture, Star House, 104-108 Grafton Road, London, NW5 4BD. Tel: 0171-813 999Reuse content