By Kate Townsend
Producer, We Have Ways of Making You Talk
The government has said it is "vehemently opposed to torture as a matter of fundamental principle" following claims by a group of MPs that Britain may be using intelligence from tortured prisoners abroad to fight the terrorist threat at home.
Some doubt whether evidence from torture is accurate
In the past though, torture has been a common tactic for interrogation, and its former practitioners say it was one of the most effective.
The Beatles music may not be an obvious tool of torture, but combine loop playing of Yellow Submarine with holding an individual under water, and it tests the endurance of most people. Hugo Garcia, the man who brought his victims to the edge of oblivion in this way, is convinced that anyone can become a torturer.
Most torturers, like Garcia, remain convinced that they are ordinary people acting under extraordinary circumstances. They do not consider themselves monsters, but instead remain convinced that you, too, would have tortured in their shoes.
The public distances itself from images of abuse recently inflicted by occupying troops in Iraq, but many of the people who've dealt out near electrocutions, mock drownings and beatings believe such techniques are effective - that torture works in getting people to talk. And some retired torturers insist they would not hesitate from doing the same today.
The stories of most torturers prove how easy it is to turn the average man into abuser. Indoctrination is often the first step towards torture. Hugo Garcia was attracted to the glamour of detective shows on television and joined the Uruguay army. He and his colleagues were told that communist insurgents were threatening the country.
They were taught the "submarino" - a technique for nearly drowning prisoners, and told it was their duty to target the opposition. In this context, the young Garcia entered the torture arena, safe that the state would take responsibility for his actions.
Other regimes have been less explicit in promoting torture, but have given their approval implicitly, by failing to punish abusers. The torturer can be safe in the knowledge that they will not be held accountable for their deeds.
On arriving in Vietnam, the impressionable American conscript Donald Dzagulones witnessed a superior prodding a pencil into the open wound of an injured Vietcong to gain information. When nobody objected, Dzagulones realised "anything goes" and embarked on a tour of duty where, as a US Army interrogator, he inflicted electric shocks on one prisoner and used dogs to intimidate other captured suspects.
Mr Dzagulones remains convinced to this day that torture is an inevitable part of war.
"I would never dream now of doing the things that I did when I was in Vietnam," he says. "The brutality doesn't stop when the shooting stops. I think torture is as much a part of war as death is."
During Algeria's fight for independence in the 1950s, French Resistance fighter Paul Aussaresses felt it was his duty to inflict electric shocks on Arab nationalists.
Like many former torturers, he still believes it is the most effective way to gather intelligence in a so called "ticking bomb" case. He claims to have stopped Algerian bomb makers from killing French civilians by extracting confessions though electric shocks and suffocation with a water saturated towel. They were methods he'd adapted from the Nazis.
The belief that torture works is justification enough for most torturers. Some experts claim that information divulged under force is always unreliable, but many who've practised torture say they have the experience to prove otherwise.
Torture, they say, is the fastest and most reliable means of forcing prisoners to divulge information.
During the apartheid era in South Africa, Gideon Nieuwoudt, one of South Africa's most notorious torturers, used a range of techniques on his ANC victims and retains a philosophical perspective.
"It's like a piano: you make use of the black notes and the white notes to make a sweet melody," he says.
He has no doubt the beatings he inflicted on detainees forced them to talk: "The people will never give you anything without torture, that I can assure you."
Former colleague Paul Van Vuuren lost count of the number of people he tortured under apartheid, but is still proud of his skills.
"There are all these movies about Rambo and stuff where they put electricity on his bodies and he's not talking. That's bullshit. There is no-one in the world; I haven't yet seen one guy that don't talk. I can take anyone on and make them talk, that's no problem."
Mr Van Vuuren, who was part of a hit squad snatching activists from the townships, had to remove any emotional connection with his victim.
"I can't say I am sorry because then I am lying. At that stage he was an object and we had to extract information out of him and we would do it to the best of our ability."
A sense of moral righteousness also eases the path to torture. Mr Nieuwoudt claims he was following God's orders by using torture to maintain the apartheid regime. But he, like many torturers, chose to keep his vocation a secret from his family.
Many torturers cite the pressure of leading a double life as the hardest aspect of their profession.
Mr Garcia in Uruguay was carried along with the belief shared by his colleagues that the prisoners were evil and, given the opportunity, would do the same to him. It was only when he witnessed the torture of a family friend that he began to question what he was doing, exposed the regime and fled the country.
Most torturers, however, continued their trade until the regime change. For many, stopping torture was not an option - peer pressure, political indoctrination and a conviction of its effectiveness ensured their participation. But the very demise of the governments under whose name they tortured is testimony itself to the fact that torture, in the long term, rarely sustains a regime.
We Have Ways of Making You Talk was broadcast on Tuesday, 5 April at 2100BST on BBC Two.