I have just read an extraordinary new book. It’s by a close and old pal whom I’d count as one of my best friends. He was my lodger in London for ten years. His book is autobiographical. And I now realise I never knew him at all.

In Don’t Ask Me About My Dad, Tom Mitchelson charts a life story that is entirely strange to me, and shocking. And yet the weird thing is that I know many of the people in it – or thought I did. His late father, Austin, who helped launch the Sunday Sport, I met and thought a likeable if flaky chap, and good company. He turns out to have been the most appalling wife-beater, liar, drunkard and debtor. His mother, whom I’d also met and who struck me as a kindly soul but a sort of ‘someone else’s mum’ character, turns out to have been the victim of a monster, in and out of women’s refuges, and someone of almost heroic fortitude.

And Tom himself, whom two years ago I would have described as a funny, sociable, laidback chap with hardly a care in the world, emerges as a tormented man, witness to terrible scenes at home, seriously sexually molested by a ghastly schoolteacher who had spotted a 13-year-old boy’s longing for a protector and mentor. Haunted and fascinated by the ability to shape-shift that this living hell had taught him, Tom turned it to advantage as a Daily Mail columnist specialising in working undercover: a confidence trickster, really. ‘I had spent the years constructing myself. I felt I was a good piece of work.’

But to the book in a moment. I first met Tom when he was an A-level student in the audience of an Any Questions? recording; he wrote to me after university, interested in journalism. I met up with him and was impressed by his quick mind, talent and personability. He started helping me with books I was writing, ending up as my lodger for a decade in a cupboard-sized room in my London flat. Tom is totally heterosexual and our 20-year friendship has been untroubled by any trace of sexual attraction in either direction (strikingly handsome, Tom was never my type) but has if anything been the more honest and intimate because of that.

Or so I thought. He never ever said a word about his father’s decades-long abuse of his mother, about the policeman’s knock, about the nights when as a small boy he sat terrified on the stairs hearing his dad shouting and her crying out, or about his schoolteacher’s four-year-long abuse of him. I’d thought they were a happy family and he’d had a normal education at an Essex comprehensive. And when – now aged 40 and happily paired with the mother of the son he adores – Tom confided that he had some bad stories of abuse from his childhood that he’d finally decided not to hide, and planned to write a book about, I thought (but didn’t say) that maybe he’d got it all a bit out of proportion.

I don’t much care for confessionals. I’d always had rather a ‘stuff and nonsense’ attitude to lurid tales of domestic abuse, and endless shock-journalism about paedophilia. I do know these things happen and don’t approve at all, but nothing like this had ever happened to me. My default response to such reports has been that it doesn’t help to dwell on things from the past or think that your present woes are all down to the fact that someone touched your bottom when you were nine.

I didn’t, however, discourage Tom when he told me of his plan to trap his former schoolteacher – by then an MBE, pillar of the church and headmaster of a British–associated public school in Kazakhstan – into a confession. He would invite him for coffee at London’s St Pancras station and secretly record their conversation. It was after all true that Tom couldn’t otherwise publish. And it was when I saw the transcript that a switch was thrown in my mind, and I knew he should go ahead.

The abuse at school was (it turned out) only part of Tom’s story, and not really the most horrible part. I had to wait for the book itself to know the whole truth. In conversation Tom had touched on it. In print it’s often as difficult to read as he found it to say. The blows, the insults, the rapes, the raised axe over his mother’s one hand (she had lost the other to cancer as a girl) had me inwardly screaming: ‘But why did you stay with him? Why did you go back to him?’ But she did, little Tom and his triplet sisters in tow. She was, he writes, ‘so deep in a hole that she couldn’t see out’.

‘I can feel the concrete of the pavement, hard on my socked feet. I heard screams coming from a little way down the road. He was dragging my mum back to the house, pulling her along by her arm. I looked around and saw neighbours watching from their windows. One or two had come out on to the street. They could see what was happening and yet acted like it was a piece of promenade theatre. The secrets of our house had spilled out on to the road.’

But in the end this is not a story of horror but of mystery. ‘I jumped to his defence so many times, yet I could have killed him myself. I was bound to him in a way I didn’t understand back then. I wish I’d had the clarity to hate him… but… I just wanted to restore the peace… to stop it occurring. I wanted to make it right.

‘He was my friend and he was my foe.’

I still don’t really understand how Tom could love his father, or why his mother just took the blows. But I know now – because I know Tom now – that real people in real life do submit when they needn’t. And if I can’t understand why, that’s my problem.