Christopher Hamilton: I'm not the man I was

Unaware of the volcanic eruption of hurt and indignation at its core, you could easily approach Christopher Hamilton's book, Middle Age (Acumen Books, £9.99), as a mere essay about chaps of 50 buying Fender Stratocasters and wearing denim.

The book is part of a series of monographs under the umbrella heading "The Art of Living", in which distinguished thinkers (including Raymond Tallis and Colin McGinn) philosophise on subjects usually considered outside the realm of philosophy – like Money, or Sex or Pets or Fame. Middle Age is offered as a rumination on the mezzo del cammin di nostra vita in all its guises: the autumnal ripeness of the self, the onset of physical decay, the failure to achieve what you dreamed of, the sense of having become a character you never chose to become.

We've been here before, many of us 50-somethings, and certainly these are fascinating themes for mature reflection, as we sit in our favourite armchair deep in our mid-life crises, and the pipe-smoke ascends through the 40-watt lamplight of our venerable study, and we nod with approval at Mr Hamilton's lively and companionable prose, his spot-on choices of quotations from Proust, Wittgenstein, TS Eliot, von Hofmannstahl...

Then you realise that, inside these calm lucubrations, a quite different book is bursting out, like the lupine snouts bursting through of the faces of the periwigged nobles in The Company of Wolves. Actually Mr Hamilton tells you on page one about the terrible thing that happened to him, that blew apart his family and derailed his life and skewed his personality and probably scuppered his marriage, six years ago. But it's only when you read on that you discover, in between the calmly objective discussions about Nostalgia or Success, how intense is his long howl of rage and dismay that human beings can treat their supposed nearest and dearest like this. You realise you're holding in your hand a new genre – the philosophical misery memoir.

It happened like this. Hamilton grew up in Portsmouth. He was second youngest of a large family of six siblings. His childhood wasn't a careless dream of innocence – his parents didn't get on, his father over-ate and his mother over-entertained gentlemen friends; they divorced when Christopher was nine and his Catholic education was strict – but at least he had his four brothers and one sister to give him a sense of grounded-ness. Then in May 2003, one of his brothers rang to make sure he was at home. "He kept leaving messages on the answering machine, saying, 'I'm coming to see you' and 'I've got something to tell you'. I thought it must be cancer. But it wasn't." What his brother told him was that the man he'd thought was his father (known in the book only as K) for 38 years was nothing of the sort; his father was another man (called only H), whom he knew, who was still alive, and who had taught him at school for several years; a family friend whose children were friends with Christopher's siblings.

Hamilton's immediate reaction was cool: "It was absolutely the last thing I expected. But my first words, when I heard, were, 'This explains so much!' I'd had, ever since my 20s, an acute but ineffable feeling of being different from my siblings. We seemed to share so much, like a sense of humour, and I couldn't put my finger on how I was different, but there it was." His younger brother was devastated. "He felt the guts had been pulled out of his childhood, everything we'd been together." Christopher knew his siblings had kept the truth from him for 20 years since K died (having sworn them to secrecy) but he didn't get angry. "It was something that ossified within the family," he says, "that simply could not be said."

The difficulty came afterwards, as he started to work out the ramifications of the news. Middle Age is a record of these ramifications: his utterly conflicted sense of self, his revulsion at being the result of a furtive affair, his rampaging self-disgust, his sudden sense of distance from his beloved siblings. He records his irritation on realising that his mother had given him the middle name Francis because all H's three children had Francis as a middle name – as if someone had been idly toying with his identity for years. He explains his shame at being a bastard, a compromised half-brother. What sound like long-pent-up feelings of fury come flying off the page as he recalls his mother taking "a perverse pride in being excessively physically demonstrative towards the men in her life in the presence of her children and others", of making him (at nine) her confidant and go-between. It's the most naked expression of family disruption since Augusten Burroughs's Running With Scissors, embedded though it is in a treatise on mid-life-dom.

Reading Hamilton's remarks about his mother's "vulgarity," her "morbid sexual intrigue" and his own sense that "sexual desire and sexual activity are polluting," one expects to meet a stern, moralising figure at his house in the suburbs of Kingston. It's surprising to find the door answered by a boyish, exuberant, ruddy-cheeked, denim-clad chap (he's 44 and looks 32) whose hair is gel-spiked like Gary Rhodes's, and who smiles and jokes through an hour of philosophy and family dynamics. He'll go only so far to explain hints in the book about his teenage years of "turmoil and despair" that made his mother disown him. "A lot of the people in the book are still alive and I don't want to hurt them gratuitously," he says. "I'll just say, I had a very unhappy childhood in various ways, and things came to a head when I was 16 or so, and at that point my mother was ... not the most supportive of people."

His sense of corruption and self-disgust, he says, "preceded my parents' divorce. Growing up Catholic, you learn that lots of things are wrong with your body." He vividly recalls a driving holiday in Scotland at 13 or 14, when he woke one night to discover his greedy and overweight father being violently sick into the bedroom sink and he was seized by "an insight into adult life as being something irredeemably squalid". His parents' appetites, for food (father) and sex (mother), left him paralysed with fastidiousness. "I think there are human beings who have a more complex relationship with their own body than other people, and I happen to be one of those."

Did he experience a feeling of relief at not being sprung from the loins of the squalid K? He looks puzzled. "No. I felt quite the opposite. I felt excluded from something I wanted to have. I felt very close to the Hamilton siblings, I liked being part of them, there was a sense of connection from which I felt excluded." And he felt invaded by his real father – "I felt this extraordinary sense of 'my God, there's this real man, my father, and whoever his parents were, I'm carrying them all inside me'."

These inner conflicts, he says, pitched him into middle age at 38. The truth of his paternity accelerated the processes of reassessment that are common for people around 40. Classic tropes of mid-life navel-gazing (who have I become? When am I most real?) took on a more vivid colouring when seen through the filter of Hamilton's new identity. "After the first storm had passed, after two years or so," he says. "I had the idea of writing a memoir of my childhood and stopping, ironically, at the age of 38. Then I got this commission on middle age: they said they wanted the series to be philosophical, but non-technical and based on personal experience. I went away and wrote 3,000 words, and it all sort of fell into place." It has, he says, been a very cathartic experience. But his chronic feelings of having no love to give have become "resolved", he says, and he admits to having met "an extremely beautiful woman", with whom he is happy and fulfilled .

After six years of twisted emotions and schizoid feelings of dissociation from his self, Hamilton seems to have reached an equilibrium. The book is dedicated to K, the man who brought him up. His real father, H, died just as he finished the book. Christopher had visited him several times, but felt no impulse to grieve his passing. His mother is still alive, buthe says it is "impossible" to have "a decent relationship" with her. She is unlikely to read his book. Meanwhile, he's just been promoted to senior lecturer in the philosophy of religion at King's College, London. He has learnt a mid-life flowering of joy in everyday things, especially walks and classical music. But he still runs a lot – five miles, three times a week – like a man desperately trying to shake off the past.

It's not every day, I said, that you find burning outrage in a work of philosophy. He smiled. "My view of philosophy is that it should churn people up. It's not about providing answers, but making people uncomfortable and making them reflect. I'm much less interested in finding answers than in finding the right questions to ask. We may all be confused by the end – but we can share our confusion in a productive kind of way."