Charles Spencer, the younger brother of Diana, Princess of Wales, has said the brutalising effect of boarding schools on people who have come to power has been devastating for society.

Spencer was speaking on the BBC’s Sunday with Laura Kuenssberg programme after the release of his memoir, A Very Private School, in which he revealed he was sexually assaulted as a child at the boarding school Maidwell Hall in Northamptonshire.

In an extract, the 59-year-old detailed the sexual assaults and beatings he experienced at Maidwell, saying they had left him with lifelong “demons”.

He said he was abused by an assistant matron at the school when he was 11, leaving him with such trauma that he self-harmed over the notion that she might leave the school.

Elsewhere in the book, Spencer suggested the impact of public school culture had made a difference to some of the people who lead the country.

When asked about this, he told Kuenssberg: “When it goes really wrong, as it did in Maidwell in the 1970s, you’re going to come out very damaged, and I know I did. And I actually say in the book, you know, to survive that, a small but important part of me had to die. And I think that’s true, you know, there was a softness that had to be trampled on, because otherwise it would be too painful.

“So if you extrapolate that and think of the damage it’s done to other people who have ended up in powerful positions – and I’m talking over the centuries, not just contemporaries – they have to have had their view of what’s acceptable behaviour, what other people mean in terms of empathy, they have to have been brutalised.

“And I cannot think that all of the effects of these schools can have been good for society, or for the empire, or whatever we were in control of at the time. I think it’s been devastating in some ways.”

In the wide-ranging interview, he revealed that his and Diana’s childhood nanny would “crack our heads together” if they misbehaved, with a “cracking crunch” that “really hurt”. He said it emphasised the “disconnect of parents”, but he did not criticise his mother and father, saying it had been “normal” to “leave it to the nanny to deal with”.

He claimed that another nanny punished his two older sisters by “ladling laxatives down them”.

In his memoir, Spencer described reliving his experiences at boarding school as “an absolutely hellish experience”, writing: “I’ve frequently witnessed deep pain, still flickering in the eyes of my Maidwell contemporaries.”

On the matron, Spencer wrote: “There seemed to be an unofficial hierarchy among her prey … She chose one boy each term to share her bed and would use him for intercourse.

“Her control over mesmerised boys was total, for we were starved of feminine warmth and desperate for attention and affection.”

As a result of the experience, Spencer said, he lost his virginity to an Italian sex worker at the age of 12.

“There was no joy in the act, no sense of arrival, no coming of age,” he wrote. “I believe now that I was simply completing the process set in motion by the assistant matron’s perverted attention.”

He also said he was beaten with the spikes of a cricket boot by the school’s Latin master.

In a statement, Maidwell Hall said it was “sorry” about the experiences Spencer and some others had had at the school.

“It is difficult to read about practices which were, sadly, sometimes believed to be normal and acceptable at that time,” it said. “Within education today, almost every facet of school life has evolved significantly since the 1970s. At the heart of the changes is the safeguarding of children and promotion of their welfare.”