Paul Vallely: A last letter seared in fierce flames

The newly discovered poem by Ted Hughes on the death of his wife Sylvia Plath is a private, raw affair

It is a long steep climb from the little Pennine milltown of Hebden Bridge to the hilltop village of Heptonstall. I once met a man who had lived there for 35 years. The locals still called him an "offcumdun" because he had been born elsewhere in Yorkshire. Memories are long in this part of the world. That perhaps explains why the tombstone of the poet Sylvia Plath, who was buried here nearly 50 years ago, is still routinely defaced.

"Sylvia Plath Hughes 1932-1963," the stone says, above the words "Even amidst fierce flames – the golden lotus can be planted." The church in whose grounds she lies is dedicated to St Thomas à Becket, a martyr, which is apt for Plath, at least in the eyes of those of her fans who blame her untimely death on her poet husband Ted Hughes, who owned a house nearby. He had left her for another woman just before she took her own life. His name has repeatedly been daubed, or even chiselled, on the granite.

The discovery this week of a poem by Hughes about Plath's final hours has resurrected the old anger at an unhappy story which has over the years been elevated to a tragedy of romantic proportions. These were star-crossed lovers. He, as dark and dour as his hometown of Mytholmroyd, down the valley from Hebden, a world where beauty and cruelty co-existed as in the eponymous "The Hawk in the Rain" of his first volume of poems. She, a privileged and preppy American, luminous and brittle, whose poetic intelligence burned, as she put it, "bright as a Nazi lampshade".

They began as a golden couple, marrying within four months of meeting at Cambridge. But from the start they consumed one another with an intensity as fierce as the vivid imagery they both deployed.

As they met Hughes decided studying literature was killing his creativity. He had a dream in which a flaming fox – an image of his raw and untutored poetic instincts – entered his room and left a burning pawprint on the unfinished English essay on his desk. Just before they parted he broadcast a radio play, Difficulties of a Bridegroom, based on a dream in which a young man runs over a hare, sells it to a butcher, and with the money buys red roses for his mistress. Plath was devastated.

Plath, for her part, used equally disturbing images. She imagined her German father "chuffing me off like a Jew... to Dachau, Auschwitz, Belsen". She portrayed Hughes as "a man in black with a Meinkampf look" – a vampire who drank her blood for seven years.

The livid nature of such imagery, along with the wracked romance of its authors, have freighted Plath and Hughes with a far heavier emotional burden in the popular imagination than the frail minds and bodies of two mere mortals can bear. They have ceased to be a man and woman and become mythic archetypes in some cosmic struggle between angry manhood and anguished femininity. Their lives have become charged with emotion, gender politics and stereotype. Hughes is the terrible husband and father. Plath is the self-absorbed navel-gazer who leaves her kids without a mother.

The truth is more complicated. Plath was not simply driven to suicide by Hughes; she had battled with depression for years, suffered a nervous breakdown and had a history of suicide attempts long before she met the Englishman. Like many strong men Hughes was weak when it came to coping with the fallibility of others, and ran away. But such a string of prosaic facts sit ill with the mythology of tragedy.

The complexity of their wild range of emotions is clear from both Plath's posthumous volume of poems, Ariel, and Hughes' Birthday Letters, a collection cataloguing the attempts he had made to work through his conflicts with Plath. They take the form of verse letters written to his dead wife over a 30-year period – but which he found too personal to publish, insisting on "slamming the door of the imagination" on her death.

They were published in 1998, the year he died, and showed him meandering through guilt, regret, perplexity and anger – with himself, but with her, too. The turmoil achieved no resolution.

What they did not contain was the 150-line poem recalling their last meeting. It was a sequence of events so unlikely, with symbolism so grim, as to seem implausible had they not happened in real life. One Friday morning Plath posted a letter to reach Hughes on Saturday morning, after her intended suicide. But, with an efficiency the Post Office would not recognise today, it was delivered that same afternoon. The new-found poem, "Last Letter", reveals that he rushed round to her house with the letter. She took it from him and set it alight. "My last sight of you alive/ burning your letter to me, in the ashtray/with that strange smile."

Two days later, after taking milk and biscuits up to the children's bedroom, and carefully taping up the door to protect them, she placed her head in the oven and the woman who had once outraged some by describing herself as "a bit of a Jew" gassed herself. In one of the Birthday Letters poems Hughes writes: "My body sank into the folk-tale/where the wolves are singing in the forest/for two babes, who have turned, in their sleep/into orphans beside the corpse of their mother". But "Last Letter" is more direct. He picks up the phone "then a voice like a selected weapon/ or a measured injection/coolly delivered its four words/deep into my ear: 'Your wife is dead.'"

It is not hard to see why Ted Hughes did not publish it while he lived. It is more a private diary entry than a poem – raw, bleeding, almost unbearable to read. "It feels a bit like looking into the sun as it's dying," said the present poet laureate Carol Ann Duffy.

Nor was it over for Hughes. Six years later, Assia Wevill, the woman for whom he left Sylvia Plath, dragged a bed into the kitchen of her Clapham flat, turned on the gas stove and got into bed with their four-year-old daughter, Shura, killing them both. An echo of Plath's own death. Perhaps this is what Hughes means in "Last Letter" when he talks of "double, treble exposure/over everything."

Whatever he had done, or failed to do, the revenge of Hughes's women on him was, the poems show, agonising. After the death of Assia and their child he wrote perhaps his greatest collection, Crow – a bleak, bitter portrait of a world teetering on the brink of apocalypse. At their heart, he told a friend, he imagined a man sitting in the desert, by a tree containing a cruel black crow. The man has a gun loaded with a single bullet. He is torn with indecision over whether to shoot the bird or himself.

The words on Plath's grave were selected by Hughes from one of the four great classic novels of Chinese literature, Monkey: Journey to the West by Wu Cheng'en. The complete quotation reads: "Even in the midst of fierce flames the Golden Lotus may be planted, the five elements compounded and transposed, and put to new use. When that is done, be which you please, Buddha or Immortal."