SERVING his apprenticeship as a writer, Robert Louis Stevenson admitted that he had “played the sedulous ape” to a number of revered predecessors, including the Williams Hazlitt and Wordsworth, Charles Lamb, Nathaniel Hawthorne, Daniel Defoe and Charles Baudelaire. Stevenson made no apologies for his mimicry; on the contrary, he regarded it as essential to his education, a pleasurable process by which he might in time find his own remarkable voice.

Muriel Spark, who follows in a direct line of descent from her Edinburgh soulmate, was similarly candid when addressing her debt to literary forebears. As a girl at James Gillespie’s school – the model for Marcia Blaine’s in The Prime Of Miss Jean Brodie – she read voraciously, ploughing through the contents of her local library in Morningside with the rapaciousness of youth. She read whatever came to hand, taking the tickets of her mother, father and brother to supplement her own inadequate supply. As she recalled: “My after-school life was divided between lending libraries and the corner of the kitchen where I curled up with my loot.”

In a real sense the library was Muriel’s university. Now and then, when I spoke to her about her past in another kitchen – that in her home in the Val di Chiana in Tuscany – she would talk about her teenage years. Her family was not poor in the breadline sense but neither had they money to burn; university, it seems, was not an option open to her. But she was ambivalent about it anyway. She might like to have gone, and been introduced formally to the canon. On the other hand, she felt that by reading serendipitously she had educated herself, which in turn had helped make her the artist she became.

I imagine Muriel wandering up and down the shelves in Morningside branch library – once mentioned in the Guinness Book of Records as the busiest in Britain – plucking books as one would apples from a bough. Here were worlds beyond her own immediate one: exotic, exciting, imaginary, fantastical, a mere stroll away from the first-floor flat in which she spent her first 18 years.

Poetry was what she read mainly. John Masefield, whom she was taken to hear read when still in primary school, and whom she met and wrote a book about in later life, was an instant favourite. She read as she would never read again – “for I was destined to poetry by all my mentors”. Wordsworth, Tennyson and Swinburne were followed by the Georgians: Edmund Blunden, Rupert Brooke, Walter de la Mare, WB Yeats, Robert Bridges and Alice Meynell, “the only woman among them”.

She was encouraged by her teacher, Miss Christina Kay, to write poetry and many of Muriel’s poems appeared in the annual school magazine. The Border ballads were an early and enduring influence, and in her 70s, with the sun going down over the Tuscan hills, she would often recite from memory excerpts from her favourites. She was determined to become a poet and took poems, such as Robert Browning’s Pied Piper of Hamlin, and attempted audaciously to improve them. Literature, for Muriel, at once respectful and irreverent, was a living thing.

These days she is best known as novelist, her ambition to be a poet thwarted by the need to earn a living. When, in 1951, she won £250 in a short story competition in the Observer newspaper her career took a path which she initially felt reluctant to take. Her first novel, The Comforters, published in 1957, was the first of seven to be written in an astonishing burst of creativity, which encompassed Memento Mori (1959), perhaps the first novel prominently to feature dementia, The Prime Of Miss Jean Brodie (1961) and, in 1963, The Girls Of Slender Means.

Critics have suggested that in the beginning she was influenced by the likes of Graham Greene and Evelyn Waugh, sharing their adherence to Catholicism and their interest in metaphysics. Of the two, Waugh, with his deft comedic touch, seems to me the better fit. He loved Memento Mori and rarely failed to mention it in glowing terms whenever Muriel sent him her latest novel. But in truth it is hard to find other novelists, stylistically and tonally, not to mention their world view, whose books sit comfortably alongside Muriel’s. She was, as her companion Penelope Jardine has said, simply “sui generis”.

The novels she most often read were French. Proust was her passion and she returned to Remembrance Of Things Past constantly. Like him, she knew that, to a writer, memory is the well that must never be allowed to run dry. She was also a great admirer of Simenon whose novels are, like hers, invariably short and driven by dialogue. Another influence was André Gide, especially his novel The Counterfeiters. In reply to letter from me about it Muriel wrote: “I could see how the type you call ‘blackmailers, thieves, two-faced schemers’ could be liberated in literature from their prototypian villainous parts without ceasing to be villains.”

But what of herself? Had she achieved what she set out to? What was her legacy? “I have realised myself,” she said. “I have expressed something I brought into the world with me ... I think I have opened doors and windows in the mind, and challenged fears – especially the most inhibiting fears about what a novel should be.”

Appointment In Arezzo: A Friendship With Muriel Spark by Alan Taylor is published by Birlinn, £12.99