There are two stark facts about British politics. The first is that it is controlled, to a degree unparalleled in any other western European nation, by a tiny, unrepresentative elite. Like almost every aspect of public life here, government is dominated by people educated first at private schools, then at either Oxford or Cambridge.

The second is that many of these people possess a disastrous set of traits: dishonesty, class loyalty and an absence of principle. So what of our current prime minister? What drives him? What enables such people to dominate us? We urgently need to understand a system that has poisoned the life of this nation for more than a century.

I think I understand it better than most, because there is a strong similarity between what might have been the defining event of Boris Johnson’s childhood and mine. Both of us endured a peculiarly British form of abuse, one intimately associated with the nature of power in this country: we were sent to boarding school when we were very young.

Staff looked on with indifference – they thought we should sink or swim (the same philosophy applied to swimming)

He was slightly older than me (11, rather than eight), but was dispatched, as so many boys were, after a major family trauma. I didn’t think a school could be worse than my first boarding school, Elstree, but the accounts that have emerged from his – Ashdown House – during the current independent inquiry into child sexual abuse, suggest that it achieved this improbable feat. Throughout the period when Johnson was a pupil, the inquiry heard, paedophilia was normalised. As the journalist Alex Renton, another ex-pupil, records, the headmaster was a vicious sadist who delighted in beating as many boys as possible, and victimised those who sought to report sexual attacks and other forms of abuse.

Johnson was at first extremely hostile to the inquiry, describing it as money “spaffed up a wall”. But he later apologised to other former pupils. He has accepted that sexual assaults took place at the school, though he says he did not witness them. But a culture of abuse affects everybody, one way or another. In my 30s, I met the man who had been the worst bully at my first boarding school. He was candid and apologetic. He explained that he had been sexually abused by teachers and senior boys, acting in concert. Tormenting younger pupils was his way of reasserting power.

The psychotherapist Joy Schaverien lists a set of symptoms that she calls “boarding school syndrome”. Early boarding, she finds, has similar effects to being taken into care, but with the added twist that your parents have demanded it. Premature separation from your family “can cause profound developmental damage”.

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The justification for early boarding is based on a massive but common misconception. Because physical hardship in childhood makes you physically tough, the founders of the system believed that emotional hardship must make you emotionally tough. It does the opposite. It causes psychological damage that only years of love and therapy can later repair. But if there are two things that being sent to boarding school teach you, they are that love cannot be trusted, and that you should never admit to needing help.

On my first night at boarding school, I felt entirely alone. I was shocked, frightened and intensely homesick, but I soon discovered that expressing these emotions, instead of bringing help and consolation, attracted a gloating, predatory fascination.

The older boys, being vulnerable themselves, knew exactly where to find your weaknesses. There was one night of grace, and thereafter the bullying was relentless, by day and night. It was devastating. There was no pastoral care at all. Staff looked on with indifference as the lives of the small children entrusted to them fell apart. They believed we should sink or swim. (The same philosophy applied to swimming, by the way: non-swimmers were thrown into the deep end of an unheated pool in March.)

I was cut off from everything I knew and loved. Most importantly, I cut myself off from my feelings. When expressions of emotion are dangerous, and when you are constantly told that this terrible thing is being done for your own good, you quickly learn to hide your true feelings, even from yourself. In other words, you learn the deepest form of dishonesty. This duplicity becomes a habit of mind: if every day you lie to yourself, lying to other people becomes second nature.

You develop a shell, a character whose purpose is to project an appearance of confidence and strength, while inside all is fear and flight and anger. The shell may take the form of steely reserve, expansive charm, bumbling eccentricity, or a combination of all three. But underneath it, you are desperately seeking assurance. The easiest means of achieving it is to imagine that you can dominate your feelings by dominating other people. Repressed people oppress people.

In adulthood you are faced with a stark choice: to remain the person this system sought to create, justifying and reproducing its cruelties, or to spend much of your life painfully unlearning what it taught you, and learning to be honest again: to experience your own emotions without denial, to rediscover love and trust. In other words, you must either question almost nothing or question almost everything.

Though only small numbers of people went through this system, it afflicts the entire nation. Many powerful politicians are drawn from this damaged caste: David Cameron, for example, was seven when he was sent to boarding school. We will not build a kinder, more inclusive country until we understand its peculiar cruelties.