Notes on a scandal: Iris Murdoch's letters to pupil who became her lover are revealed for first time

February 1964, and a portly female lecturer in early middle age sits hunched beneath a Goya print in her top-floor office at the Royal College of Art (RCA), marking scripts. In the corridor, a man 20 years her junior hovers, waiting to be invited in to discuss his thesis. Within moments, David Morgan would be standing before Iris Murdoch. Little did either know this meeting would signal the start of a relationship of increasingly emotional encounters and a correspondence whose tone would veer from passion to acrimony over a period of three decades.

Theirs was an unlikely love story: she was a successful 44-year-old writer with seven darkly philosophical novels to her name, and a critical reputation to match; he was a penniless autodidact who'd spent time in a school for maladjusted boys and a mental asylum, before blagging his way into art school on the strength of a hastily scribbled outline of his left foot. But what ensued between Murdoch and the young man she would affectionately refer to as "dear boy" and "my child" was to achieve, for a time, the intensity of a full-blown affair.

Now, details of this tempestuous 31-year relationship are being laid bare with the release of a trove of intimate letters from one of Britain's most respected novelists to her former pupil. In With Love and Rage: A Friendship with Iris Murdoch, a personal memoir by Morgan out tomorrow, he sheds light on an association that, until now, has been explored only in scattered references in an earlier biography of the writer.

Though now a respected lecturer himself, at Chelsea College of Art and Design, 46 years after he first encountered Murdoch there is still something of the outsider about Morgan. Home is a rented maisonette festooned with bohemian clutter on the top floor of a 19th-century townhouse in west London. As I'm ushered into the lounge by a pretty woman in her thirties, Morgan approaches, hand extended. Yet he seems nervous as he gestures to a velvety sofa, its back lined with plastic dolls' heads. Is this his work? "No, it's not my work!" he snaps, adding after a pause: "The severed heads – OK... I put off letting my lady have a child for many years, and as a substitute I bought her freakish dolls' heads from Portobello Market. The girl who let you in – when we had a child, she was that child." (Morgan tells me his "lady", Pauline, is painting upstairs.)

Niceties over, our conversation turns to Murdoch. But if I'm expecting to have to tease information out of him, he soon proves me wrong: "I only realised Iris Murdoch was in love with me by re-reading her letters. Anne Rowe [Murdoch's official archivist, and author of the introduction to With Love and Rage] said something very astute: she said Iris Murdoch always had to be in love with somebody. I think I had that privilege in 1964 and 1965."

Morgan refers to the first two years of their friendship as "what I now realise was a love affair". After that initial encounter in her office, they began meeting regularly, sometimes twice a week, he normally visiting her at her flat in Harcourt Terrace, near Earl's Court in west London or at a nearby pub. It was at the former, within a month of that fateful supervision, that they first kissed. "She wanted to see my artwork," he recalls of the pretext for his visit – described in his memoir as leading to a fumbled embrace which "happened spontaneously" over an art book open to a page on Piero della Francesca.

Clumsy or not, the first of nine Murdoch letters reproduced in the book (from a stash of 200 Morgan has "in a box upstairs") suggests the kiss affected her profoundly. In the letter, dated 20 June 1964, she writes: "I had intended, earlier, that we should part for the vacation on rather more formal terms. But by last Wednesday it had become impossible not to touch you & to draw you a good deal closer – and perhaps it's surprising we held out so long with only Piero della Francesca between us like a drawn sword."

The same letter contains several other sensuous lines, including one in which Murdoch alludes to Morgan's "singularly good-looking head", and a passage in which she hints at previous romances: "And I want this to be 'clean-cut': I too have had so many muddled & twisted relationships, and I want ours to be steady & clear, & I think it can be. (I have, by the way, mentioned your existence in general terms to John Bayley [Murdoch's husband], who trusts me absolutely & never wants to hear details. All that side of things is OK. I was touched and pleased that it occurred to you.)"

Bayley and Murdoch had married in 1956, shortly after Murdoch's affair with the Nobel Prize-winning author Elias Canetti. With Bayley elevated to the post of English professor at Oxford, the couple settled at the nearby village of Steeple Ashton. But, while they remained there happily for 30 years, and together until Murdoch died in 1999, he was long-suffering about her periodic flings, and the impact some of them are thought to have had on her work. Canetti, for instance, is widely seen as the inspiration for some of the devilish male enchanters present in Murdoch's darker novels, including her Booker-winning The Sea, The Sea (1978).

Morgan returned to Murdoch's letters after being contacted by Peter Conradi while the latter researched his sprawling 2001 biography Iris Murdoch: A Life. He describes With Love and Rage as less a memoir than "a collage of letters, fragments, conversations, anecdotes and meditations".

Of their "love" phase – which lasted barely two years of their 31-year friendship – Morgan evokes vivid memories, including the intensity of Murdoch's kissing. They would, in general, cosy up in "her room" at Harcourt Terrace – "the place where we had little snacks, sat with art books, sipped whisky, broke the ice and were gradually so overwhelmed by each other that we kissed". But once, at a party, in the midst of a row with the girl he was pursuing at the time, he recalls ' drunkenly punching Murdoch as she stepped between them. "Not here, David – later," was Murdoch's immediate and ambiguous response to the incident. Reflecting on it in his memoir leads Morgan into a near-hallucinogenic passage, in which he agonises over whether they ever did stray into erotic waters: "the faintest taste in the way she kissed me of something lascivious... just the movement of a tongue perhaps".

While such extracts are undoubtedly intimate, With Love and Rage is quite chaste by the standards of today's "kiss-and-tells". And, though there is much tenderness in the book, its descriptions of Murdoch's appearance are far from flattering. She is depicted as a tweedy "Joan of Arc" with "middle-age spread" who "rolled when she walked", and whose trademark "page-boy haircut" had become a "ragged helmet". When pressed for his first image of her, Morgan recalls "a short woman with a red peasanty face".

So why was he so attracted to her? In the book, he describes how, when they first met, they both "experienced a momentary epiphany". Asked to elaborate, he says: "She was a phenomenon. Something 'came off her' I've never felt from anybody else. It was like coming into a presence. There was a tremendous goodness about her."

This goodness would manifest itself as charity. Morgan had reached the RCA against the odds, all but disowned by his working-class parents and only by "begging" its then professor of paintings, the eccentric Royal Academician Carel Weight, to let him in. From early life, Morgan had been in, as he puts it, "the awkward squad". He had won a scholarship to public school, only to be expelled for refusing to "fit in". Next stop was a school for maladjusted boys, then Stratford's King Edward VI Grammar School. He left at 16, barely scraping two O- levels. A tense period back home ended with his being briefly admitted – "completely sane" – to a mental asylum.

Murdoch's upbringing – middle-class, progressive education, Oxbridge – had been altogether more comfortable, and she recognised this. Though her early letters to Morgan show impatience at his unwillingness to take on menial work to pay his way through vacations, she repeatedly bailed him out. Even the night of their first kiss ended with her "slipping a £5 note into my jacket pocket because she knew I was hard up".

So how did her "love" switch to "rage"? Morgan feels he gave her enough provocation with previous bad behaviour, but Murdoch's anger erupted over a single, shameful if overblown, incident about which he remains sheepish: he boasted to a fellow student that he could rely on Murdoch's favouritism to guarantee them both good marks for their theses. When the horrified student threatened to leave college, Morgan confessed to his mentor – who, in a ferocious letter, chastised him for "a kind of cruelty I've never met before".

Morgan had glimpsed Murdoch's rage earlier when, contrary to her explicit instructions, she discovered that he had kept their correspondences: "When she got mad, it wasn't just because she saw a pile of her letters. Beside them was a pile of [carbon copies of] the letters I'd written her."

Yet the row over the theses was different, and though they would exchange letters for a further 29 years, their meetings would become rarer and briefer: "I thought she'd finished with me, but she wrote and said, 'I've taken you on as a friend.' She'd said the punishment would be five years, but it was three months. But she never unburdened herself in the same way again." Did they still kiss? "Yes, but it got less. And I think she gradually slid out of love with me." Why does he think she stayed in touch? "What kept it going was her voyeuristic interest in my love life and her need to help me."

This takes the conversation on to Murdoch's writing and its exploration of the darker aspects of human relationships. Morgan had other, turbulent love affairs and was occasionally violent (his memoir details "girl-slapping" and "tussles with men"); in exchange for her generosity, did Morgan allow Murdoch to draw on his experiences for her fiction?

In life, Murdoch dismissed any suggestion that she based her complex characters on real people, but her biographer Conradi, whose latest book, Iris Murdoch: A Writer at War: Letters and Diaries 1938-46, came out last month, explored the notion that Morgan may have influenced some ingredients in her books. He maintains the view that the "moral anarchists" she met at the RCA fascinated her because their hedonism was so alien to anything she had experienced before.

Anne Rowe, director of the Centre for Iris Murdoch Studies at Kingston University, whose in-house press is publishing With Love and Rage, goes further, arguing that Murdoch's fascination with Morgan took her close to complicity: "In many ways, Morgan's sexual imbroglios would have been a moral anathema to her, but she thirsted for experiences that lay beyond her own. It's here that the memoir touches on a fascinating aspect of the moral jeopardy that perhaps haunts every writer's life. I'm sure that in her relationship with David she crossed moral boundaries she set herself – it was certainly erotically charged and his darkness excited her."

Yet Morgan has no time for such theories, spluttering: "Oh dear! It's sweet of them but Anne Rowe's PhD students have gone on a Morgan hunt in the novels and found me in them when I'm sure I'm not. I wasn't that important."

Murdoch, he says, admired the emotional distance writers such as Shakespeare and Dickens kept from their characters, and is adamant that Murdoch's were simply "made up" – though, pressed on whether elements of his emotional entanglements might have surfaced in her books, he concedes: "Yes, I would agree with that. I think she loved intrigue."

But Morgan disagrees with AN Wilson's portrayal of her as "two Irises". In Iris Murdoch as I Knew Her, Wilson described a political division (from her early communist leanings to her later conversion to Thatcherism) and a sexual one (between apparent bluestocking and alleged bed-hopper). For Morgan, there was, more simply, "serious" Iris and "silly" Iris. He disagrees with the idea that "Oxford Iris" was the sensible one, and that in London she indulged in escapism among her wild associates. Rather, he paints her London self as a maternal angel of mercy, darting around the capital dispensing free-flowing financial and emotional support to impoverished, sometimes suicidal, ex-students. "Oxford was her comfort zone. In London, she had a huge gang of people she came to help. None of us knew each other, but we were all in some kind of trouble. She gave us money, time and conversation."

Morgan recalls noticing "hints" that Murdoch might have other confidants and dependents ("she was always off to see someone else"), but nothing prepared him for Wilson's revelations about her alleged flings, which initially felt like "unfaithfulness". He's since rationalised them as "a special kind of promiscuity connected with being an only child".

Does he think Murdoch had other long-term soulmates? "I think there are a host of correspondences that haven't come out – unless they've destroyed them, or not cared enough to keep them." And was he in love with Murdoch? He inhales deeply, frowns. "I was in awe of her. Even if you're in love with somebody in the present you often don't know it, do you?"

With the heady days of the RCA, and the early phase of his friendship with Murdoch, behind him, Morgan's domestic life slowly stabilised. By 1974, after dating Pauline for some years, the couple had moved in together. They remain in the same flat, near Ladbroke Grove station, to this day.

Morgan's last memory of Murdoch is of seeing her off on a train from Paddington in 1995 after the latest of what had, by then, becoming increasingly infrequent and hollow lunch meetings. He remembers her seeming "a bit doddery". Within months, she was diagnosed with Alzheimer's disease. "She only half-knew who I was. Even though she couldn't help it, it makes you feel abandoned. To protect myself, I toughly abandoned her. That last meeting wasn't some kind of, 'Oh God, we'll never see each other again.' It was a meeting between two people who hardly knew each other any more."

'With Love and Rage' (KUP, £12.99) is out tomorrow

Straight from the heart

In her letters to Morgan, Murdoch's emotions moved from infatuation in 1964 to a sense of betrayal after 'this wretched business' – Morgan told a fellow student that Murdoch would give them good marks

Late 1964

My dear child,

It was splendid to see you. I do love you. Thank you for showing me the bell [Morgan had scoured London for real-life motifs from Murdoch's novels] – that was wonderful! Some god must have led you to it. I was feeling so tired yesterday, but simply touching you made the tiredness go away.

I was so glad to find you (somehow and so evidently) "whole" again. You have much health and strength in you. Please get us the Welsh record. I enclose the £2 it will probably cost. Also, do examine your financial situation and let me know if you need anything to keep you going. I hope one of the jobs materialises. In case you have any freedom in the choice of times, keep in mind that I am in London during term from Tuesday morning or afternoon till Thursday afternoon. But if you have to absent then you have to & we must think our way round that. I want those photographs of your "angel" some time. I'm sure you have a most remarkable painter inside you. I embrace you.

Ever, I

April 1965

Dear David,

I'm not going to "abandon" you (unless you wish it) but we must make another start on a different basis. I know I have a responsibility for this disastrous friendship & I stand by my mistakes. But you are a very dangerous person to have for a friend, & it would be very irresponsible of me (as well as psychologically impossible) to go on as before. (God knows what lies you have told about me in other quarters.) I don't want to see you at present. (I feel I would simply have nothing to say to you.) There had better be an interval during which the impression left by this wretched business can fade a little. I will send you a note in the second half of term & will see you then, if you want to see me.