Tom Perry was watching a film in his boarding school gymnasium when his French master leant over and whispered: “I might come to your dormitory tonight.” It was a Saturday evening and Perry, then 11, was elated. He imagined that, as one of Caldicott's sporting elite and golden boys, he might have been selected to be taken somewhere special as a weekend treat.

True to his word, Peter Wright, the teacher, did come to the dormitory in the early hours and told Perry to make his way to his private room. When the boy did so, he found Wright lying in bed.

Perry's account of what happened next is grotesque. The teacher lifted the bedcovers to reveal that he was naked and sexually aroused, and invited the child to get in. Unsure what else to do, he did so. He says that Wright put his tongue in his mouth and kissed him, then indecently assaulted him and made the boy do the same in return. When Wright was satisfied, the bewildered child was dismissed back to his dormitory.

So began a routine of abuse, says Perry. Wright, also the rugby and cricket master, who was hero-worshipped and feared by the pupils in equal measure, was often reckless in his greed. He would request that Perry bring his morning cup of tea up to his room, which he did in view of the whole school, then get the boy to masturbate him. During other, longer sessions with Wright in bed, the teacher would tell him about the sexual relationships he was having with women, often making disparaging remarks about their bodies. It was a secret world, a foul cocoon. But it was not a one-off. And Wright was not the only teacher abusing children.

A remarkable new documentary funded by the Channel 4 British Documentary Film Foundation will paint a picture of Caldicott in the 1960s and early 1970s that will shock those who have only ever regarded it as an elite educational bastion in Buckinghamshire which acts as a feeder for schools such as Eton and Harrow. Three former boarders, now in their fifties and at the school at different times, relate their stories about being abused by three different teachers.

The Caldicott they describe is one where a culture of child abuse flourished, where the teachers enjoyed such deference from parents that their word was rarely challenged, where a stiff upper lip and no whingeing was the medicine for most misfortunes, and so a few men could gorge themselves on several boys at any one time. It is an unexpurgated insight into how the abused child's value system and sense of self is ripped asunder, and how such children always feel complicit.

None of the three complained to the authorities at the time because, they say, they were silenced by shame, fear and a confused sense that they must be to blame. Victim guilt is central to paedophilia's ability to prosper, they say, and it kicks in immediately. Besides, in their contained world, the teachers were the authorities. That sense of shame persists today - but is now accompanied by fierce anger that their lives have been so damaged by it.

Alastair, a writer and editor, was first targeted at the age of 11 by Martin Carson, then a science teacher and now a convicted paedophile, who went on to sodomise him. Incredibly, Carson was caught in the early 1970s and Alastair admitted that he was a victim. But the headmaster managed to assure his father that it was a “blip”, there was a cover-up and Carson was sacked without the police getting involved (it was nearly 30 years later that he would be imprisoned for his crimes).

That headmaster, who had risen through the teaching ranks, was Peter Wright. It was decided that the best thing for Alastair was to get straight back on the rugby field.

Mark Payge, now a writer and business consultant, attended the school between 1957 and 1963. He was singled out by another teacher who cannot be named (he was never charged, as police believed that they would be unable to secure a conviction) and abused on a daily basis until it became part of his life. Today Payge says that a part of him still cannot believe that he managed to become accustomed to it. But “once you get over the disgust of being abused by a big, hairy, smelly adult man, you can do it ... over and over again,” he says. “You have been groomed and you feel ... well, your parents don't want you because they have shipped you off to the Gulag ... and this guy seems to really like me.”

Like Perry, he, too, was soon engaged in a monstrous parody of a normal domestic routine. Tasked to wake the master each morning in his room (it was common practice for pupils to wake masters at some boarding schools), Payge says: “I would take off my trousers and he'd get me on his stomach and stimulate himself and passionately French-kiss me.” He likens it to being “ridden like a blow-up doll”. The teacher always tasted of whisky. It was disgusting, he says - yet a part of him valued the feeling of being treated differently from other boys.

All three men now realise how sophisticated the grooming process was, gradually breaking down boundaries in small ways until the perpetrators were ready to strike. Perry remembers Wright inviting his favoured boys into his room to watch television, where they would drink the dregs of his whisky nips. Wright encouraged the boys to sit next to him, on the arm of his chair. “He would then ask you to stroke his neck,” says Perry. “I remember that he suffered quite badly from boils on the back of his head.” At other times Wright would show favouritism by giving certain boys a lift to rugby matches in his car. He also touched Perry's bottom.

Each time another subtle line had been crossed, until the children were “softened up” to physical intimacy.

In Payge's case his abuser “bonded” by behaving as childishly as the boys he taught, enjoying scatalogical humour with them and playing practical jokes on other boys. “We would all then fall about laughing,” says Payge. “He was in on the joke. [The teachers] behaved like children.”

On another occasion his abuser helped Payge to cheat in a maths exam by giving him the papers. He also recalls having “highly inappropriate” sexual conversations with Peter Wright in which it would be openly acknowledged that Payge was sleeping with a teacher, although Wright himself never abused him. “I'm pretty much convinced that they had conversations about [which boys] were on each other's menu,” says Payge.

His conversations with Wright would take place in Wright's bedroom. “We would joke about the size of [my abuser's] penis,” he says. “There was a disassociation from reality.”

But there was also a sense that there was nothing particularly wrong with such behaviour. None of the teachers told the boys that they must keep it a secret: this was apparently what happened in boarding schools. It was no big deal and, actually, if you were one of the “chosen” boys you were lucky because you were in the favoured elite and other boys envied you.

“It was a ghastly cycle,” says Perry, “but you step out of it at your peril. Do you step out into the chill wind of this scary bastard, or do you want the sunshine on your back?”

It should be said that a criminal case against Wright never came to trial and he has always denied the allegations, which he continues to do. More than 30 years later, Perry and four other boys who claim that they were abused by Wright came forward to the police, and Wright was charged with 13 counts of indecent assault and three counts of gross indecency with a child between August 1964 and May 1970. But in 2003 a judge stayed the case as an “abuse of process”, ruling that the alleged offences had happened so long ago that Wright could not get a fair trial.

Today Wright, in his late seventies, lives near Caldicott. Through his solicitor, he has said that he does not wish to make a response other than to confirm that the allegations were denied in the course of the police investigation and continue to be denied by him. Contacted by The Times this week, his solicitor said that he had been unable to speak with Wright but “would be surprised if my client would wish to add to that statement”.

In a statement, Caldicott school said: “Caldicott's current headmaster, teachers and governors have great sympathy for the men who were pupils at this school between 30 and 40 years ago, who gave harrowing personal testimony in the film Chosen. A school should be a place of safety for the young people in its care. It is over 35 years since the events recalled in the film, and the current staff at the school is now entirely different. In common with all top schools, Caldicott has a wide range of measures in place designed to avoid the risk of child abuse.The 2008 Independent Schools Inspectorate report described both pastoral care and governance at the school as outstanding.”

Perry was incensed at the judge's decision to block the case, because many children find it impossible to report abuse while it is going on and often while their parents are still alive (Perry and Payge could bring themselves to go to the police only after their parents' deaths).

According to Payge, his abuser was eventually reported by the school matron. But, asked by his father whether he had been abused, Payge still said no. “The abused always ends up protecting the abuser,” he says. “It was a defining moment in being groomed; he had broken me, I was no longer connected to my family, to the truth.”

Many years later, when he did complain to the police, he was told that it was uncorroborated evidence and too much time had elapsed. But Payge says that he just couldn't do it while his parents were alive: “There was an unconscious impulse to protect them from this awful thing ... and that they had fed me to the lions.”

Only Alastair has seen his abuser convicted. Twenty-seven years after Carson had been dismissed for abusing boys, Alastair went to the police and he was tracked down. He had been teaching at The Harrodian School in London. Carson admitted indecent assault and possessing indecent images of children. In 2003 he was sentenced to two years in prison. He was released after a year.

Is it likely that the teachers concerned were themselves abused as children? Payge says that it wouldn't surprise him. Some of the teachers, he said, “behaved like children”, as if they were in arrested development: “They were absolutely insatiable ... dysfunctional people.” But they were clever enough to know that the parents also needed to be “groomed”, turning on the charm with them.

If one's parents are close to and in awe of an abuser, the child is even less likely to tell. Payge, who describes his father as “a relentless social climber”, had to suffer his parents inviting his abuser and Wright to dinner at their home in the school holidays. He became a “split person”, he says, who had to shut down emotionally to function. Yet such is the complexity of child abuse and the confusion it wreaks that he felt betrayed when he found that he wasn't the only one - that his abuser had other boys on the go.

“There was a chap that slept next to me and one night I told him I had heard that [my abuser] was sleeping with some boy. ‘Who isn't he sleeping with?', he replied.” Payge felt utterly betrayed. When the teacher was eventually accused, and later dismissed, he felt gratified - but only because, as he puts it, “he hadn't honoured the commitment I thought he had given me”.

Forty years on, although all the men have partners and children, the abuse has taken its toll. Alastair wrongly assumed for many years that he must be gay, Payge found it hard to have committed sexual relationships with people and was a drug user for a while, and Perry told no one about the abuse until 2000, when, he says, he blurted it out to his GP. It was the prelude to a bout of depression.

During our interview he was close to tears several times, partly from anger and partly, I suspect, from impotent rage. Now he campaigns for better child protection policies in schools.

Alastair says that time does not heal: “You can never forget. It is embedded in your psyche - it can be a smell, a sound, a memory: you're reminded every day.”

More people are expected to come forward as a result of this film. Whether they do or not, these men have taken a colossal step by speaking out publicly after so many years hushed by shame. As they now know, there is no greater friend to the paedophile than silence.

True Stories: Chosen, September 30 at 10pm on More4, www.chosen.org.uk