Instead of a Book, By Diana Athill

When the poet Edward Field suggested to Diana Athill that she publish the letters she had written him over 30 years, her first response was "nonsense!". But when he sent them to her to look at, she started laughing. "I thought 'Oh, my God!'" she told me in an interview last year. "Those letters were really an extraordinary portrait of a friendship and my life."

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You could argue that we don't need to know all that much more about Diana Athill's life: that she has, in the six memoirs she has already published, and the many pieces written for newspapers, and the many interviews she has given, particularly after becoming a "celebrity" in her nineties, already said quite a lot about a life that has borne witness to a big chunk of history. You could argue that we've already heard about the writers she worked with during her 50 years at Andre Deutsch, and about the pain that, for many years, shaped her private life, and the affairs she had to numb that pain.

If you did, you wouldn't be wrong. We have heard a great deal about Athill's life as one of the major editors of the 20th century, and about her upper-class upbringing, and the fiancé who rejected her before he was killed in the war, and her relaxed approach to sexual fidelity, and her relationships with a string of Caribbean men. But that's to forget, until you encounter it again, the sheer joy of her brisk, wry and hugely energetic prose.

"Diana has a physical need to write," says Field in his introduction. Her letters, he says, are "full-blown literary works". They certainly are "literary works", glittering with sharp-as-a-silver-scalpel observations about people and events, and with the cool wit that turns even "frightful" situations – mechanical breakdowns, domestic disasters, family illness – into comic cameos that have you longing for more. But the physical need to write is also evident.

"There now, I've written that down so I needn't think of it again!" she says, after describing the ordeal of an acquaintance who was tied up and raped. In a later letter, she quotes Field's own words about writing: that "half" of it is "learning to put down what is there." This is writing not just as maintenance of a friendship, but as catharsis and habit.

Most of all, it's writing as the product of an almost relentlessly clear-eyed gaze. "None of them seem to recognize a beady eye when they see one," she complains when the reviews of her memoir Make Believe come out. It's hard to see how they could have missed it. Athill brings the same cool eye to friends, lovers and colleagues as she brings to the "gnomelike" builder who "recognized us at once as two times the sucker than just one of us would have been," and to the "bossy boots to end all bossy boots" who helped her when her car broke down in France. When she writes of a friend with warmth, you know that she must really, really like them.

The writing, as always, combines upper-class English matter-of-factness with a self-deprecating humour that's often (and sometimes slightly irritatingly) exacerbated by the use of Random Capital Letters For Wry Emphasis. As an editor, Athill would know she doesn't need them, but she wasn't writing for publication, and is too scrupulously correct to remove them now.

It's also, as always, imbued with the kind of honesty that sometimes makes you gasp. "No woman I saw him with," she says, of someone she used to know, "including myself failed to fall into bed with him almost on sight". It's hard to think of many writers who would relegate their own experience to such a casual aside.

"I've decided," she writes in 1986, "that it's a waste of precious time to think about getting old". As the years pass, and the ailments stack up, it's impossible not to. It's because they stack up too much, in the end, that she decides to cut off publication in 2007. The "detailed swapping of symptoms", she says, becomes "boring". Maybe, in other hands, it does. But I'm not sure that Diana Athill could write a boring word.