Most books by academics are relentlessly impersonal. Footnotes buttress with hard evidence any statements that are remotely controversial (and sometimes many that aren't). Acknowledgments may contain thanks to the author's wife for help with the proofs or index, but otherwise one would never know that the writers were flesh-and-blood human beings with relationships, passions, prejudices, hopes and dreams.

So what happens when academics buck the trend, turn confessional and decide to reveal intimate - and often embarrassing - details of their personal lives? Take John Sutherland's Last Drink to LA (2001). This certainly draws on his talents as a literary scholar in some sharp reflections on writers, masculinity and alcohol, and some vivid character sketches of the strange types one finds in Alcoholics Anonymous groups in the US. But it also gives a frank account of the time when his own life hit the skids, when his chronic alcoholism led him to hear voices coming out of kettles and paintings on the wall, and a bender left him "in the grip of agonising withdrawal. Uneven heartbeat, panic attacks, dislocation of time".

His lurch downwards, just before he signs up at AA, reaches its nadir while working at Caltech in Pasadena. The only place for a drink "within cycling distance (at least, cycling back distance)" turned out to be a gay bar. He had always been heterosexual, although an inadequate and unfaithful husband, but this seemed a chance to try something new. After one heavy night, he recalls, he woke up semi-dressed beside an African-American - and "my hand brushed against his penis (accidentally, as I trust), and felt nothing there ... His Johnson had been cut off, amputated. Perhaps it was a preliminary to a sex-change operation".

This, unsurprisingly, was "the end of (his) night and the morning of clarity. Was this what it had come to? All that grind, the degrees, the books read and the books written? Holding the penile stump of someone I barely knew, in a God-forsaken California ghetto in a sun-baked country where I didn't belong?" The reader might also have some questions: is this really the kind of story one wants to hear about a distinguished professor? And why on earth would he want to tell us?

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Self-revelatory books have some obvious attractions. They can potentially attract a far wider readership and larger royalties than most scholarly monographs. They represent a different kind of writing challenge. And for those who have established careers and can afford to give offence, they provide ample - and often highly entertaining - opportunities for settling scores.

Terry Eagleton's memoir The Gatekeeper (2001) is equally sharp and outspoken about the nuns of his Catholic childhood, the leftist splinter groups where "venereal infections (circulated) almost as rapidly as theories of neo-colonialism", and the "students agitating for reform to the English Literature syllabus to chants of 'Remember Che!'" Yet some of his fiercest satire is reserved for the "querulous narcissism" of his former Oxbridge teachers and colleagues. One tutor "was certainly intelligent, but had no more ideas in his head than a hamster. Indeed, he was not only bereft of ideas but passionately opposed to them, which struck me as a little odd for a doctor of philosophy ... It did not do to be too clever, and the trick was to find a way of speaking about Heraclitus or John Stuart Mill which Princess Margaret might understand".

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It is safe to assume that most young academics would avoid writing like this about potential employers. Another danger is giving hostages to fortune.

Take, for example, Eric Hobsbawm's largely political memoir Interesting Times: A Twentieth Century Life (2002). This is full of vivid vignettes such as "the night train to London", on the day the Second World War broke out, which was "full of tall, long-legged blondes: the English dancers from the Folies Bergere and the Casino de Paris ... returning to their homes in Morecambe or Nottingham". Yet he is well aware of his reputation as "a professor who likes jazz and remained in the Communist Party longer than most", so it is unsurprising that one looks for what he has to say on the latter theme. "The Party," he writes, "had the first, or more precisely the only real claim on our lives ... If the Party ordered you to abandon your lover or spouse, you did so." He accepted the official "line change" in autumn 1939 "that Britain and France were as bad as Nazi Germany", despite being Jewish. He would certainly, he tells us, have agreed to work as a Soviet agent.

Most extraordinary of all, he admits that he "became essentially a nineteenth-century historian, because I soon discovered ... that, given the strong official Party and Soviet views about the twentieth century, one could not write about anything later than 1917 without the likelihood of being denounced as a political heretic". For anyone wanting to dismiss his writings as propaganda rather than objective history, Hobsbawm has provided them with all the ammunition they could possibly require.

Similar issues haunt two powerful and even more recent memoirs by academics. At 13, John Cornwell was well on the way to becoming a hooligan - he had nearly killed the boy next door with a cricket bat and even tried to derail a train - when he began five years' training at a remote and now defunct minor seminary as the first step towards ordination as a priest. Seminary Boy (2006), written entirely from memory, vividly captures the beauty and intensity of a life punctuated by ritual, the all-consuming but illicit "special friendships", the "material and emotional dependency", the racking guilt as he struggled (often by thinking of the English martyrs of the Reformation) against "impure thoughts" and "irregular motions of the flesh". At least one priest was openly abusive and there is a terrible scene where another boy, deranged by earlier molestation, becomes obsessed with the idea of "becoming the cross on which Jesus was nailed".

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Cornwell is now director of the Science and Human Dimensions Project at Jesus College, Cambridge, and has written books about Coleridge, miracles, Prozac and science under the Nazis, as well as three acclaimed and bestselling books about the Papacy - A Thief in the Night, The Pope in Winter and Hitler's Pope - that have not always pleased the faithful. But, despite writing with painful honesty about masturbation, high camp "crushes" and sexual fantasies, he loved working in a more confessional mode and feels that some things can only be described from the inside. "The problem of writing about religious experience, in which I'm deeply interested," he told me, "is that with an objective, scientific or even historical approach the subjective element is almost by definition neglected. Hence it requires a confessional approach. As far as I know, nobody had ever written a full and frank personal account of life in junior seminaries in England."

While the seminary undoubtedly "saved and made" a boy with otherwise dismal prospects, it also left Cornwell with strong but very conflicted feelings about the Catholic Church. Those who want to discredit his criticisms of the popes can suggest they are just the expression of a personal agenda. He has also had some raised eyebrows from colleagues who were "mildly shocked at the idea of anyone exposing themselves so much in print. John Carey, professor of English at Oxford, wrote in his (very enthusiastic) review of the book that there were a great many things that most people would rather forget about themselves. A woman at my college said: 'I've learnt rather more about your willy, John, than I ever wanted to know!'"

Very different in spirit is the recent memoir Making Trouble: Life and Politics (2007) by Lynne Segal, anniversary professor of psychology and gender studies at Birkbeck, University of London. A lifelong radical, Segal is unsympathetic to the vogue for "abuse memoirs", with their stories of "solitary transcendence" and "triumph over trauma", and set out to produce an upbeat, if sometimes wry, account of collective political activism and the causes she has been involved in. "I wanted to write," she told me, "a type of generational account of how radicalism from one period does, or does not, influence that of another, how experiences/memories of events are written over, even destroyed, given the critical role of place/time in all radical affiliations."

Making Trouble has its share of footnotes and grapples with well-known theoretical issues that Segal describes as "the slipperiness, even inevitable incoherence or self-deceptions, accompanying self-presentation" and "the pitfalls, the instabilities, contradictions and overall inadequacies of claiming any identity confidently". "To what extent is it possible," she asks, "to offer a portrait of a political moment, placing oneself within it, however cautiously, knowing the limits of retrospection?"

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Yet, spurred on by her publisher, Segal accompanies such self-questioning with a great deal of exuberant and sometimes intimate detail. She gleefully reports her (undeserved) reputation as "the woman who lives in a four-storey house with a different lover on each floor". A moving personal and reflective chapter about ageing and the "physical wilderness always threatening to enclose the older woman" ends with the first shoots of a new love affair: "My fingers, if not always my legs, stay crossed."

None of these books is remotely "academic" in the traditional sense and they no doubt attract hostility for it. Nor, despite lovely moments of bitching and gossip, are they in the least bit cheap or salacious. All are works of reflection and analysis as well as revelation. But they also acknowledge a central truth that when it comes to drink, sex, politics and religion, dispassionate sifting of evidence may be all very well, but many of the most interesting insights will always come from people who've actually been there and done it.

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