THE winter of 1963 was the coldest on record in a century.

Before dawn on the morning of February 11, in a spartan, underheated flat in a fashionable area of London, Sylvia Plath turned on the gas taps in the oven and laid her head inside it on a neatly folded towel. When her still-warm body was found a few hours later, Plath's children, two-year-old Frieda and nine-month-old Nicholas, were safe in their bedroom upstairs. Towels had been stuffed under their door, and their window was wide open. On their bedside table were glasses of milk, and bread.

The night before her suicide, Plath had been visited by her doctor, who knew she was in a dangerous state of mind. He arranged for a nurse to visit the next morning at nine, and hoped that, with the children in the house, Plath would not do anything overnight to risk their safety.

He misjudged, as had others. First among those to accuse himself was poet Ted Hughes, Plath's estranged husband, from whom she had separated five months earlier, after discovering he had been having an affair.

As Hughes wrote to his sister Olwyn after learning of his wife's death: "I was the only person who could have helped her, and the only person so jaded by her states and demands that I could not recognise when she really needed it." To his brother Gerald he added: "No doubt where the blame lies."

Reading Plath's letters from the weeks before her death, and judging by the comments of her friends, it's not hard to see why someone might not appreciate just how close to the edge she was. Adept at putting on a brave face, and also veering between manic highs and the depths of despair, her mood changed almost hourly. The worst time – as her death bears out – was 5.30 in the morning when she would take her first anti-depressant of the day. These would begin to take effect around 7am. Yet despite her deteriorating state of mind, she could also write to her mother, in the months after she and Hughes parted, and talk of her relief at being free, of being happier than ever before, and of her great plans for her writing future.

These were no castles in the air. Already, Plath had a glittering reputation. In 1956, when she first met Hughes, the son of a Yorkshire tobacconist, this highly strung, middle-class Bostonian was a Cambridge Fulbright scholar: she was beautiful, talented and her poetry was highly acclaimed. Clever, attractive and enigmatic, she and Hughes made a golden couple, and married swiftly.

In September 1962, immediately after Plath and Hughes had separated, and before she moved from their Devon home to London, she wrote feverishly, producing 40 strikingly original poems, now immortalised in her collection, Ariel. Dark, angry and electrifying, they are among the most powerful poems of the 20th century. The exhaustion any writer would feel after this outpouring would have been cause enough for mental collapse, but a combination of other fateful factors all, in hindsight, contributed to her breakdown.

Among them was the low-key reception of her first novel, The Bell Jar. This fictionalised account of her attempted suicide 10 years earlier was published pseudonymously, a few weeks before her death, to a muted response. Around the same time, two American publishers politely declined to publish it.

Then there was the recent death of an old neighbour in Devon, which brought flooding back her despair over her own father Otto's death when she was a child. Otto held a malign influence over her. She felt he had abandoned her, and when Ted and she parted, she saw it as a second desertion and betrayal.

On top of all this came the unbearable snow and ice, during which she and the children struggled with colds and flu. It is one of the small, chilling details in her final weeks that, on arrival in London in December 1962, having locked herself out of the new flat, Plath had to insist that a gas oven was supplied. "The obliging gas boys climbed on the roof and jimmied a window and installed the stove," she told her mother cheerfully, with no hint of sinister intent. As well as having no electricity, which was an easily fixed problem, the flat had no telephone, which was not.

But all was not misery. According to Hughes, he and Plath had been discussing getting back together. He reported this to Plath's mother a month after her suicide. "Think of how it must be for me too," he said, in a rare moment of self-pity. But this most stoical of men quickly recovered himself. "I don't want ever to be forgiven," he continued. "I don't mean that I shall become a public shrine of mourning and remorse, I would sooner become the opposite. But if there is an eternity, I am damned in it."

Sadly, he did not need to wait for the next world for judgment day. The tragedy of Plath's suicide was hijacked, and the facts distorted, to suit the purposes of people far more heartless than the man they considered Bluebeard. The untimely death of the young, lovely and talented is always fodder for myth-making but the ingredients in the Plath-Hughes story were so spectacularly juicy, they inspired a thousand half-baked rumours and accusations that were as vicious as they were unfair – to all parties.

Even his staunchest allies would admit Hughes was a magnet for ill-fortune. Assia Wevill, the woman he had been seeing before his break-up with Plath, had a child with him. In 1967, in a savage echo of Plath's act, Wevill killed herself and their four-year old daughter. For the feminist Furies, here was conclusive evidence that Hughes was a chauvinist monster.

In the years after Plath's suicide, and in the wake of Wevill's, he endured the equivalent of a feminist fatwah as outrage grew over his perceived role in Plath's death, and his iron-fisted control of her work. While sensible readers, feminist or not, embraced Plath for her literary brilliance, extremists ignored the inconvenient fact that Plath had a history of suicidal depression, and claimed her as a martyr for their man-hating cause.

One can see how Plath's story could be twisted to fit a radical feminist agenda. Outwardly the model wife and mother, she could very easily be portrayed as a genius whose talent was thwarted by a domineering, jealous husband. That Hughes was his wife's literary executor further fuelled suspicion of his meddling with her work before publication. His destruction of her last journal, as he claimed to protect his children, was seen as sacrilege.

Even without Plath's depressive personality, it would be unusual for such intense and brilliant poets to live long and happily together. Their household, in many ways loving and stable, was also a cauldron of emotions. Probably the greatest cause of conflict, before Hughes's affair, was Plath's growing neurosis over her long-dead father, whom she hated and revered. As Hughes wrote in his poem The Table, of the writing desk he had made for her: "I did not/ Know I had made and fitted a door/Opening downwards into your Daddy's grave."

But for those who appointed themselves jury over this marriage, there was no room to acknowledge the grey areas of real life. Hughes was an adulterer and Plath, like every wronged woman before her, was a victim of a patriarchal society of double standards. While she was sacrificing her art to her domestic life, her lionised partner was playing the field. No-one appeared to consider that, as a highly educated woman who employed a nanny to allow her to write, Plath was unlike most ordinary women. Whatever else she was, it was not a drudge or doormat.

Would Plath's feminist champions have felt differently had they known that before she and Hughes separated their heroine had made a pass at another man? Probably not. To her defenders, it was simple. Hughes's desertion led directly to her suicide. Thus onto Plath's slim shoulders was put the weight of centuries of female hurt at men's infidelity. This was further compounded by a profound sense of loss that such a champion of women's issues had been cut down in her prime. The combination of glamour, sex and tragic death as well as Plath's indubitable genius made for one of the most intoxicating, powerful myths of modern times. No wonder it has endured.

Much of this, of course, was unjust. No-one – not even the protagonists – fully understands what goes on in a marriage. But when mental fragility and unresolved psychological problems complicate the situation, reason and rationality are often the first casualties.

Contrary to what the feminist lobby wanted to believe, Plath was, for much of the time, far from unhappy. Neurotic, certainly. Temperamental – what writer isn't? But for all her demons and doubts, she was profoundly contented with her children, her home and her increasing literary prowess. As her close friend, the critic Al Alvarez has said of her astonishingly intense late poems, "they are full of life, not death". And, as someone who himself had survived attempted suicide, he always maintained Plath had hoped and intended to be found before she died.

Had Plath's suicide not succeeded, the feminists would have lost a patron saint. She was no use to them alive. Without a thought for the pain they were inflicting not only on Hughes but on his and Plath's children, they set out to ruin his reputation, and in the process damaged all those in his and Plath's ambit. No onlooker can speculate why their son Nicholas committed suicide in 2009, nor why he had such a long history of depression, but one thing is sure: the feminist decrying cannot have helped. The childhood of Frieda and Nicholas ended not with their mother's death, but the day Plath was adopted as a feminist cause celebre. And as a recent spat over a missing acknowledgement in Plath's posthumously published work shows, even now it takes little to ignite fresh recriminations and rekindle the controversy.

In the 1960s and 1970s, as the furore raged, Hughes was almost unable to go out in public. He was issued with death threats and was ambushed by placard-carrying protesters, be it in Aberystwyth or Adelaide. He once regretfully turned down an invitation to read at an event in Edinburgh to honour Norman MacCaig, saying the publicity he would attract would ruin the evening. He was even openly accused in print of beating and murdering Plath. Meanwhile, her headstone, in a country graveyard near the Hughes family home in Yorkshire, was repeatedly vandalised, her married name rudely scratched out.

In the face of intolerable provocation, Hughes stayed silent. Writing to Plath's biographer, Anne Stevenson, he explained his omerta: "I preferred it, on the whole, to allowing myself to be dragged out into the bull-ring and teased and pricked and goaded into vomiting up every detail of my life with Sylvia for the higher entertainment of the hundred thousand Eng Lit Profs and graduates who ... feel very little in this case beyond curiosity of a quite low order, the ... popular bloodsport kind."

Not until the publication of Birthday Letters in 1998 did he break cover. These intimate, searching poems, almost all addressed to Sylvia, were his celebration, and mourning, of her. The collection, which is among his finest work, was published only when he knew he was close to death.

One of the cruel consequences of Plath's suicide is that her work, and Hughes's, has been overshadowed by their almost Shakespearean tragedy. For 50 years no-one has been able to read their poems without remembering what the authors suffered. Some, indeed, cannot bring themselves to read Hughes, or Plath, as the case may be. And readers are always expected to take sides.

This is, in itself, little short of a tragedy. Plath's writing is diminished if read as an extended suicide note. While The Bell Jar is a gripping if uneven first novel, her poetry is in a class of its own, pyrotechnic work that lies far above gossip and speculation. With Hughes, the sombre, almost primitive power of his work, rooted in the English soil, speaks for itself.

The controversy that continues to smoulder around their names does a great disservice to both, reducing them to players in a soap opera, rather than two of the world's finest poets. Those who have claimed Plath as a martyr to the feminist cause rather than a literary giant could not have more demeaned her had they wanted to blacken her name rather than burnish it.

Reducing her to a victim misses the essence and vitality of her personality. Her work is the howling cry of a woman who will not be defeated or dismissed, who lashes out at a painful world, rather than suffer in silence. The flesh as well as the bones of this woman, who once described herself as "over-exposed, like an X-ray", can be found in her poems. There, thankfully, she remains breathtakingly alive.