'I tell you I've written a great book," DH Lawrence informed his publisher Edward Garnett, after sending him the manuscript of Sons and Lovers in November 1912. "Read my novel – it's a great novel." Lawrence's immodesty is forgivable: the book had been through four drafts, and after two years of struggle he was hugely relieved to have it finished. The sense of elation didn't last long. He worried about the title (he had originally called the book "Paul Morel"). He worried whether it might benefit from a foreword (and belatedly posted one to Garnett). He worried about the dust jacket, and arranged for a friend, Ernest Collings, to design one (like the foreword, it wasn't used). Beneath these worries lay a deeper worry, about the text itself: "I am a great admirer of my own stuff while it's new, but after a while I'm not so gone on it," he admitted. He was already on to the next thing (a draft of what would become The Rainbow), and had "scarcely the patience" to correct the proofs. But he was proud when a finished copy reached him in Italy. And the word he used to Garnett recurred, in letters to friends. "It is quite a great novel"; "I remember you telling me, at the beginning, it would be great. I think it is so."

Lawrence was right. Sons and Lovers is a great novel. A century of readers have reached for the same adjective. FR Leavis did, when he enrolled Lawrence in the "great tradition" of the English novel, comprising Jane Austen, George Eliot, Henry James and Joseph Conrad. And Philip Larkin did so, too, describing Lawrence as "England's greatest novelist" and Sons and Lovers as his finest achievement: "Cock me! Nearly every page of it is absolutely perfect." The perfection wasn't apparent to those close to Lawrence at the time, including his childhood sweetheart Jessie Chambers, his editor Garnett, and his wife-to-be Frieda, all of whom suggested improvements and left their mark on the finished text. But the reviews were good, and 100 years later the novel's reputation holds up, despite the recent dip in Lawrence's critical standing.

To anyone of my generation, that dip is a puzzle. In the early 1970s, when I was studying at Nottingham University, Lawrence was hot. (I can't pretend that my main reason for choosing to go to Nottingham was that Lawrence had been there before me, but I'd been a fan of his work since filching a copy of Lady Chatterley's Lover from my mother's bedside cabinet at the age of 14.) Partly it was the films: Ken Russell's Women in Love appeared in 1969, Christopher Miles's The Virgin and the Gypsy in 1970. Partly it was his pertinence to feminism: Kate Millett's Sexual Politics put him at the centre of undergraduate debates about misogyny, patriarchy and the myth of the vaginal orgasm. Partly it was his politics: was he a hero of the sexual revolution or a fascist and colonialist? The attacks on him grew fiercer as the years went by, but to me the difficulties he posed were evidence that he mattered. From Nottingham I went on to write an MA thesis about him at McMaster University in Canada, which boasts a Lawrence archive. The thesis doesn't bear rereading, but the best of Lawrence, including his poetry, travel books and essays, remains as fresh as ever. Surely he cannot remain unfashionable for long.

For those new to his work, Sons and Lovers is the place to start. Though it came after The White Peacock and The Trespasser, it reads like a first novel. This isn't only because it's life writing, recreating scenes from the author's own experience. Nor is it because the story concerns childhood and adolescence and all that go with them, including fear, shame, self‑consciousness, emotional hypersensitivity, sexual awakening, and the hubristic certainty that (as Paul Morel puts it) one is "going to alter the face of the earth in some way". There's also the freshness and intensity with which Lawrence presents the Morel family – as if this was the only family in the world where the parents don't get on, the father drinks, the mother resents her son's girlfriends, money is short, art and literature become a refuge, and so on. At 27, Lawrence was well-educated and widely read, but the style of Sons and Lovers is wonderfully unknowing – no distancing English irony breaks the spell. Irony wasn't in Lawrence's nature, and at the time he wrote the book he didn't have the leisure for it anyway.

He began drafting the novel in October 1910 and completed it just over two years later; in between, he ended his long relationship with Jessie Chambers, became engaged to then broke with another girlfriend, Louie Burrows, lost his mother to cancer, fell seriously ill with pneumonia, gave up his teaching post in Croydon, returned to Nottingham, and fell in love and eloped to Europe with Frieda Weekley, the wife of one of his professors. All these crises fed into the novel. Few texts have been more "over-painted". As Frank Kermode has pointed out, this is what Lawrence wanted, for his novel to be organic and open to experience, "liberated from the burden of finality and completeness placed on it by his enemies, the novelists who, in his opinion, mistook structure for life, and novelistic custom for natural law". But by the standards of the time, Sons and Lovers was in danger of seeming loose and discursive, which is why, when he sent the typescript to Garnett, he insisted "it has got form – form", and why Frieda felt obliged to add a postscript to Lawrence's letter making the same point ("any new thing must find a new shape, then afterwards one can call it 'art'") .

Mother load … Sarah Lancashire and Rupert Evans and Gertrude and Paul Morel in a 2003 TV adaptation of Sons and Lovers

To the 21st-century reader, the anxiety over possible formlessness seems odd. At times Sons and Lovers is almost too deliberate, too symbolic, too controlled. The episodes in which the three most important women in the novel, Mrs Morel, Miriam Leivers and Clara, respond to flowers, for instance, and thereby reveal their different characters, are so carefully patterned as to risk losing the "felt life" that Leavis thought Lawrence's greatest gift. (Mrs Morel is practical-minded about flowers – "Now, just see those … Haven't they done well"; Clara the sensualist thinks they look better growing in the wild than when picked; the possessive Miriam faints and fawns: "To her, flowers appeared with such strength she felt she must make them part of herself.") But such structural patterns are rarely as simple as at first appears.

The novel, Lawrence explained to Garnett, "follows this idea: a woman of character and refinement goes into the lower class, and has no satisfaction in her own life. She has had a passion for her husband, so the children are born of passion, and have heaps of vitality. But as her sons grow up she selects them as lovers – first the eldest, then the second. These sons are urged into life by their reciprocal love of their mother – urged on and on. But when they come to manhood, they can't love, because their mother is the strongest power in their lives, and holds them."

The sexual bond between mother and son is established early on. "Paul loved to sleep with his mother," we're told. When she accompanies Paul to the interview for his first job, at Jordan's factory, she behaves "like a sweetheart" and both of them feel "the excitement of lovers having an adventure together". "Why can't a man have a young mother?" he exclaims, "I'll never marry while I've got you." The incestuous undercurrents come to the surface in chapter eight, with a "long, fervent kiss". If we're unsure what to make of the kiss, the drunken Walter Morel, returning home, leaves us in no doubt: "At your mischief again?" he snarls. In the aftermath, father and son nearly come to blows. But Mrs Morel forestalls them by fainting, and while Paul comforts and revives her Walter stumbles off to bed. "Don't sleep with him, Mother," the son pleads, and in doing so recognises that "he still loved his mother best". All this is unashamedly autobiographical. As Lawrence told a friend when his mother lay dying: "We have loved each other, almost with a husband and wife love." Jessie Chambers similarly reports him saying: "I've loved her, like a lover. That's why I could never love you."

It seems certain that by the time he finished the novel, Lawrence was aware of Freud, had grasped the basics of psychoanalytic theory, and would have heard through Frieda of the term "Oedipus complex", even if he hadn't read the relevant essay. But in the text itself any such framing knowledge is set aside. Of course, Lawrence knew that Paul's mother-complex was not unique – he described it as "the tragedy of thousands of young men in England" – and by giving Mrs Morel the name Gertrude he alludes to Hamlet, whose hero also suffers from an Oedipus complex. When, within a few years of the novel being published, certain critics treated it as a case study, he was furious: "My poor book: it was, as art, a fairly complete truth, so they carve half a lie out of it, and say Voila. Swine!"

If Sons and Lovers is, as art, "a fairly complete truth", Garnett must be given some credit. Indignant scholars have caricatured him as a middlebrow hack who brutally lopped away a tenth of the novel, prudishly censored its erotic passages, and forced Lawrence, in a huff, to take his next novel elsewhere. But the letters Lawrence wrote to Garnett show that he trusted his judgment and felt grateful for his support – so much so that he dedicated the novel to him. Garnett, who also encouraged Joseph Conrad, Ford Madox Ford and Edward Thomas, was one of the least conservative literary figures of his day. In a sense he had been waiting for Lawrence, long before he found him. In a review of Arnold Bennett's Grim Smile of the Five Towns in 1907, he complained that modern fiction had more to reveal "about the life of the Kaffirs, the Malays, the Hindus, than about the life of Yorkshire miners, the Lancashire millhands, or the Staffordshire 'black country'". It was no wonder Garnett felt excited when Lawrence sent him a draft. Later he wrote of Sons and Lovers that it was the only novel "of any breadth of vision in contemporary English fiction that lifts working-class life out of middle-class hands, and restores it to its native atmosphere of hard veracity."

None of the cuts Garnett made removed the hard veracity of Lawrence's dialect words – a point in his favour, since other London editors would surely have done so. He pared back passages about the young William, at the risk of betraying the plural "sons" of the title, but mostly with a gain in focus and narrative pace. With one notable exception, the censorship, too, is innocuous. "She had the most beautiful hips he had ever imagined," Lawrence writes, when Paul sees Miriam naked for the first time. Garnett changed "hips" to "body", which seems to me an improvement, "hips" being an odd thing for Paul to focus on and, I suspect, a euphemism. The one serious misjudgment Garnett made concerns the scene where Paul and Clara go back to her mother's house, after a night at the opera. Too late for the last train back, Paul is invited to stay over. Frustrated by the mother's refusal to go to bed and leave them alone together, he reluctantly makes his way upstairs to Clara's bedroom, where he undresses. Garnett cut the following few lines:

"Then he realised that there was a pair of stockings on a chair. He got up stealthily, and put them on himself. Then he sat still, and knew he would have to have her. After that he sat erect on the bed..."

A braver editor might have allowed Lawrence both his double entendre and the authentic resoluteness of a man on heat ("he would have to have her"). But the real censorship concerns those stockings. Too kinky, Garnett must have reasoned. The sensible Clara might have thought the same, had she known what Paul was getting up to in her bedroom, and not responded to him as warmly as she does when he creeps back downstairs and finds her naked in front of the fire. (Garnett trimmed several sentences from this scene too, including a reference to Paul holding a large breast in each hand, "like big fruits in their cups".) Still, for us it's an insight into Paul – a clue to his feminine side, perhaps, or closet transvestism, or masturbatory male heterosexuality, or, on a deeper level, his need to know what it feels like to be Clara. The modern reader wants the stockings, and will wonder why Garnett didn't dispense with the Mills & Boon cliches instead ("She gave herself. He held her fast. It was a moment intense almost to agony"). But by making Sons and Lovers a novel which, unlike The Rainbow, escaped moral denunciation and legal writs, Garnett did Lawrence a service.

Sexual awakening … Clockwise from above: Mary Ure (Clara) and Dean Stockwell (Paul) in the 1960 film adaptation. Photograph: Allstar/Cinetext/

Jessie Chambers did him a service, too, when she looked at an earlier draft of the novel and made suggestions as to how he might make it more truthful ("I thought what had really happened was much more poignant and interesting than the situations he had invented"). But when he showed her a subsequent draft, she was "bewildered and dismayed" by the portrayal of Miriam, who was based on her – "I felt that I had suffered a terrible inner injury" – and concluded that he had "handed his mother the laurels of victory". Perhaps his greatest treachery was to have made Miriam so frigid; when she's not quivering, swooning, wheedling and going off into trances, she's described as "stiff". At any rate, when Lawrence sent Chambers the galley proofs, she returned them unread and severed all contact with him.

Not only does Paul's account of Miriam's sexuality seem unfeeling, his intellectual contempt for her is brutal. As Kate Millett puts it: "The scenes of his condescension are some of the most remarkable instances of sexual sadism disguised as masculine pedagogy which literature affords." Both she and Chambers suppose that Lawrence means to endorse Paul Morel's interpretation of events – whereas his attractiveness as a hero and reliability as a narrator are, in truth, open to doubt. "You are a nun," he tells Miriam, but Clara puts him straight about this, ("she doesn't want any of your soul communion. That's your own imagination. She wants you") and the accusation carries little weight given his own timidity and priggishness. Paul might not honestly face up to things, but the novel does. Trust the tale, not the teller, Lawrence famously said, and in Sons and Lovers this means trusting ourselves to derive meanings that neither the hero nor the narrator offer up. The profusion of detail, the use of dialogue, the multiple viewpoints: all these ensure that the novel will know more than the novelist knows.

That Sons and Lovers is more than the story of Paul Morel is established from the beginning, since the early scenes, perhaps the finest in the novel, in effect predate him. When a pregnant Mrs Morel is shut out of the house at night, and later when her husband flings a kitchen drawer, cutting open her forehead and causing blood to drip on the new baby, Paul is not there, as a cognisant witness, to tell us what happened. Sometimes the novel's voice is that of an omniscient narrator. But mostly it's narrated from within – and can switch abruptly from one character's consciousness to another's. These days, aspirant novelists are told to be consistent about point of view, not to leap about as Lawrence does. Yet the method works – and is crucial to the enlargement of the novel's moral universe.

Lawrence came to think that he had done his father an injustice in Sons and Lovers. And certainly mother and son gang up against Walter and denounce him as boorish. But as readers we warm to him more than they do. He may approve of William's fiancee because she doesn't like reading – "Er's like me … Er canna see what there is i' books, ter sit borin' your nose in 'em for" – but he's good with his hands, can sing, dance and tell stories (he holds his children spellbound with tales from the pit), and speaks in a dialect full of spark and humour. When Lawrence created Mellors, the gamekeeper in Lady Chatterley's Lover more than a dozen years later, he was doing penance for Morel: the two names are virtually anagrams of each other, and the two men burn with the same "sensuous flame of life".

The portrait of Clara is compelling, too. Depicted as a woman "made for passion", there's far more to her than her body – not least her tough-minded criticisms of men. Though Paul might wilfully ignore Clara's involvement in the suffragette and socialist movements, the reader can't. Clara offers a feminist reading of her lowly status, Mrs Morel belongs to the Women's Guild and bemoans her economic dependence and Miriam, too, complains of the opportunities denied her through the simple fact of being born a woman ("I want to do something. I want a chance like anybody else"). Lawrence may not give feminism the platform it deserves (there are no scenes of Clara making public speeches, nor any praise for Miriam's efforts to educate herself), but he registers its presence nonetheless.

The same can be said for his treatment of politics. As Terry Eagleton has pointed out, the year 1912, when Lawrence finished the novel, saw the largest ever miners' strike in Britain, with further unrest the following year, after the worst pit disaster in a century. These historical events are absent from the book. And yet the realities of working-class life intrude more forcibly than in any other novel of the modern period. Morel's daily routine; his injuries; his clashes with pit managers; the look and layout of the pit village of Bestwood – all this is brought out in meticulous detail, and though Lawrence did not, as later in his career, spell out his stated antipathy to industrialism, "the condemning of the workers to ugliness, ugliness, ugliness", he embeds it in the story. It's taken for granted that success for Paul, as for William before him, will mean leaving his birthplace. "In writing Sons and Lovers Lawrence was not just writing about the working class but writing his way out of it," Eagleton says. But writing his way out didn't mean dishonouring his caste. His portraits of miners and laceworkers are drawn with inside knowledge, without caricature or condescension.

Miriam's appeal to Paul is tied up with where she lives, and for all his complaints about her neediness he is still extricating himself from the relationship in the novel's last pages. Indeed Lawrence briefly teases us with the possibility of a romantic ending by bringing the two together again: with Mrs Morel out of the way, will Paul finally see Miriam for what she is, not as his mother sees her? It isn't to be. The novel ends with Paul on his own, turning away from the darkness and walking "towards the city's gold phosphorescence", an ending which most critics read as "open", but which seems to me unambiguous in its opting for life rather than death.

Before Paul can escape towards the light, he first has to murder his mother. Murder may seem too harsh a word, since she has cancer and this is a mercy killing, but Lawrence is careful to emphasise Paul's impatience to put her out of her misery. Long before he administers an overdose of morphine, he is wishing her dead. "Mother, if I had to die, I'd die. I'd will to die," he says, once it's clear her condition is terminal. Lawrence doesn't debate the moral dilemma of euthanasia, describing the act as one of "sanity". But Paul's behaviour seems characteristically self-absorbed. Once his mother is no longer capable of nurturing him, she can safely be sacrificed; to put it less brutally, whatever she may feel about lingering on, he will not allow the pain and loss of dignity.

Though Leavis praised Lawrence for being "on the side of life", death brought out the best in him. "You have to have something vicious in you to be a creative writer," he once said. The "softness" of Sons and Lovers – an effeminate hero and all that swooning over flowers – is balanced by scenes of male violence involving Walter Morel, when drunk, and Baxter Dawes. Hardness is there in the dialect, too: guttle, kested, barkled, cozzly, butty, chelp and so on. In his next novel, The Rainbow, he began to turn inward, away from a solidly recognisable external world with "vivid scenes", objects depicted "in the powerful light of emotion" and the "old stable ego of the character". It could be argued that the shift is already there in Sons and Lovers, Part 1 of which (set in childhood) is stronger on physical detail, whereas Part 2 (set in adolescence) charts a landscape of emotional vacillation. Another way of putting this would be to say that the first half of Sons and Lovers belongs in the tradition of the Victorian novel, whereas the second half shows Lawrence moving towards modernism. It is a difficult novel to classify, whatever the terms – not quite a Bildungsroman, a novel of growing up, since Paul isn't exclusively the focus of attention; nor a Kunstlerroman, a novel about a writer or artist, since Lawrence, unlike Joyce in Portrait of the Artist as a Young Man, treats aesthetic aspirations as secondary to an emotional and sexual education. "Gothic" or "pastoral" won't do, either, though there are elements of both. Perhaps "social-realist" comes closest, though not if it implies Dickens or Trollope. "A book which is not a copy of other books has its own construction," Lawrence wrote. He was remaking the English novel, which is why Sons and Lovers fits none of the categories.

"If Lawrence had been killed off after writing that book," Larkin said, "he'd still be England's greatest novelist. If one knocks out all his books except Sons and Lovers and Lady Chatterley he is still England's greatest writer." Greater than Shakespeare? Maybe not. But it's true that those two novels, published at either end of his career, are his most naturalistic and physically intimate. Lady Chatterley's Lover is a messianic novel, a tirade against those who "do dirt on sex" – and a plea for men and women to be more "in touch". The earlier novel doesn't preach to the same degree, and is the better for that, but addresses the same question: how can we live richer, more fulfilled lives? A massive theme, which few novelists then or now would dare to take on. Yet he succeeded triumphantly. There is nothing quite like Sons and Lovers in the whole of literature. It is momentous – a great book.