Eden with all the snakes

Perhaps the best autobiographical writing needs to have something slightly indecent about it. It is mainly when reading diaries, those great uncooked lumps of sensibility, that the most avid and curious of readers can occasionally feel a sudden flush of vicarious shame, a furtive conviction, like the one that comes when talking to an emotional drunk at a party, that one is being told more than one quite wants to know about the workings of someone else's soul.

But then, it may be that the power to induce this vertiginous sensation of dismay is a mark of the authenticity of the emotions and the writing involved. At any rate, the effect is produced by some tremendously distinguished writers. In Boswell, Rousseau, Tolstoy and, more recently, John Bayley's accounts of his life with Iris Murdoch, there are plenty of passages at which one catches one's breath or even finds oneself at first refusing, like a horse, to clear the candid obstacle.

There is a fair sprinkling of such moments in Diana Athill's fragments of memoir. Between 1963 and 2000 she produced four volumes of autobiography - most recently Stet, now out in paperback (Granta, £7.99) - and now there is a fifth, Yesterday Morning. This book, subtitled A Very English Childhood, is described by its author as "the material at the bottom of the reservoir - the stuff which, on the whole, causes a person to be what he or she is". There is something ominous and disagreeable about this description: it calls to mind the dried-blood sediment that settles in old wine or the vile dreams that surface at a certain stage of psychoanalysis. All of which is entirely misleading, for although this is a book written in the shadow of extreme old age, whose "big event - the thing," as Athill puts it, "which replaces love and creativity - is death", it contains little that is murky and no sense that these are the last wringings from the reservoir. On the contrary, the writing is limpid, vigorous, often blissful, though invariably tempered with Athill's East Anglian (or is it upper middle-class?) asperity.

Athill was born in 1917 and spent much of her childhood at her grandparents' 18th century house in Norfolk. She thus grew up in a culture and atmosphere - that of the minor English country house - which is now as decisively extinguished as the cavalry charge or the civilisation of Ancient Egypt.

Among the many vanished luxuries of that environment was the opportunity it provided for children to inhabit an imaginative universe parallel to, but mostly separate from, that of adults. Thus if your parents' marriage was not happy, as Athill's parents', on the whole, was not, you would be aware of the fact, but as a single strand of narrative among all the other dramas of person and place - the grandparents, aunts, cousins and servants; the lake, the kitchen garden, the ponies, the dressingup box, the attic - which together made up the story of your life.

"Everything important in my life seemed to be a property of that place," Athill writes. "Beauty... animals... books and all my other pleasures; safety... my knowledge of good and evil and my wobbly preference for good." It sounds like Eden; so, of course, there are snakes. Athill writes with her habitual heart-stopping candour of the nastiness of children, their - or rather, her - snobbish, indecent and bullying tendencies. And then she writes with exactly the same candour, at once forensic and gossipy, about her parents' marriage, their sexual incompatibility, her mother's affair ...

Which raises, once one has stopped wondering how the old lady would have felt about having her most private crevices thus elegantly displayed, all sorts of interesting questions about the extent to which one possesses the narratives of one's own life. It is the narrative of her own life that entrances Athill. As long as her subject is herself, she sparkles. Only in the brief passages when her gaze turns towards the world beyond her mind's window does the writing betray signs of faltering or inflexibility. Which may be a symptom of great age, or perhaps it is merely the captivating and entirely ruthless egotism of a born confessional writer.