Literary reputation is a fascinating thing: how it waxes and wanes. The long shelf of the 20th century positively sags with books by writers whose names are already within an inch of being forgotten, whose publishers now struggle to shift their once acclaimed and bestselling titles, or even to keep them in print. After the biography has been delivered – and let us pray it arrives throbbing with love affairs – a library hush sets in. The estate must scrabble around a bit: perhaps the journals will prove a minor hit, or the juvenilia, stuck between hard covers with a few previously unseen photographs. Or what about the letters? Everyone loves a witty letter. Can’t some professor with a sabbatical to take zip between Texas and Oxford and gather them all up?

Iris Murdoch ticks all these boxes. Celebrated in her lifetime, the diminution of her achievements began – as she had feared it would – soon after her death in 1999, helped on its way by her husband, the Oxford academic John Bayley, who revealed to the world her Alzheimer’s disease and thus put her sprawling later novels in a different light. In 2001, Peter J Conradi published an authorised biography, and in 2003, AN Wilson, a friend, gave us an “anti-biography”; both detailed her affairs with men and women, and the former was much praised. After this, however, quiet fell. Murdoch still has her fans and, aware of their endangered species status, they can be extremely ardent. But it’s undeniable that she’s little read now. Something about her emotionally frantic world – its archness, its paradoxical want of feeling – fails to connect with 21st-century readers.

Will Living on Paper, a new collection of letters from Murdoch, send people back to her? I cannot believe that it will, and though it’s heartening to see Chatto & Windus taking her seriously, another part of me wonders why it, rather than a university press, published this volume. As promisingly fat as it is – Murdoch devoted four hours a day to her correspondence – its contents are irredeemably dull and frustrating. If it does not illuminate her writing, nor does it much expand on her private life, save for to remind us how ruthless she could be in affairs of the heart, how very gelid when in a corner, or about to do a U-turn (don’t be misled by the popular idea of her as an otherworldly super-brain, all wide eyes and surprise). Though the letters cover the war years, when she worked as a civil servant, and the period of austerity that followed them, when she was a philosophy don at Oxford, you’ll find among its pages no vivid accounts of bombed-out London, of the egg-less privations of high table. What Murdoch does mostly in these letters is emote, loudly and repetitively and self-centredly – and the more she does this, the less you believe in her. Even when she was at her most insistent about her feelings, I had the sense that her affairs were a control mechanism. The terms friend and lover were, for Murdoch, interchangeable – and sometimes the upgrade from one to the other came only when she doubted a person’s loyalty (she was not, by the way, at all loyal herself, at least not when it came to sex).

The earliest letters date from the late 30s and early 40s, when she was at school and then a Cambridge student, and her parents were living in Blackpool (“there are great crowds of people, yes, and they all sound like Gracie Fields”); the last, effortful and much shorter, from the 90s, by which time she was beginning to lose her mind (“I began a letter and then lost it. I don’t know where I am. I am trying to think”). The most interesting are written to Brigid Brophy, the (younger, married) novelist with whom she had an affair in the 60s. Murdoch writes that she thinks of herself as a “male homosexual in female guise”, though what this meant in practice so far as Brophy was concerned had less to do with sex – “I’m not in love with you, and don’t want to be” – than with a peculiar role play involving Raffles, EW Hornung’s gentleman thief: Murdoch assumed the role of the amateur cracksman, while Brophy was cast as his accomplice, Bunny, formerly his fag at school. But if this suggests their relationship had a certain levity, do not be deceived. It was tortured: sadomasochistic in an emotional sense, if not a physical one (“You are not a true classical sadomasochist like me,” noted Murdoch, having confessed that she had wanted to be beaten by those who interested her. “You are just an abnormal perverted one.”). Brophy was needy – too needy – and thus Murdoch is always apologising half-heartedly for her failings, her transparent insincerity shading swiftly into relief when her lover eventually moves on. It’s striking that Brophy was open about her dislike of Murdoch’s novels. As she (Iris) points out: “I am, I think, rather like my books, so that it is at least odd (and a little unnerving) to find you detesting them.”

The book also includes letters to the more famous of her male lovers, among them the writer Elias Canetti – though oddly none to Bayley – and we get a sharp taste of her politics, most notably in a letter to the Times in which she bemoans Labour’s plans for comprehensive education (a traditionalist who moved to the right as she grew older, she was in favour of grammar schools).

And by way of light relief? I’m afraid there’s not much of that here. I laughed only twice. First, there is the moment when she describes, in a letter of 1965, how Bayley and “all other New College senior members of the English School, with the exception of David Cecil” [Lord David Cecil, esteemed biographer of Jane Austen] have received super-advance copies of a disgusting new magazine called Penthouse. It was the detail that Cecil was “very dashed” not to be among them that got to me. Second, there is the letter of 1990 she writes to her new best friend, Josephine Hart, praising her novel, Damage. Murdoch’s encomium to this torrid and very silly little book makes for hilarious reading whether you take its extravagant blandishments – “it is a tour de force… at intervals, one positively shuddered” – at face value, or not.

Living on Paper is published by Chatto & Windus (£25). Click here to order a copy for £20