He was a mod. That much I can say for sure. Four-button Madras jackets, buttoned high; Ben Sherman shirts, Sta-Prest parallel trousers that in Newcastle at that time were known as "parallels" or "strides". There was a vogue for wearing desert boots that started around 1963 or 1964, and a way of walking that involved spinning an invisible stone away with the outside of the left foot, and then the right. The left foot and then the right. A hunched-shouldered, duck-toed walk that seemed to come naturally to the footballers at the school. Was MacSweeney a footballer? I don't remember. He was an athlete, though; a runner. Long-legged. Clean limbed. Not poet material at all. (Not even a poet of the cool school, supposing we had known what that was.)

He had the walk: head down, toes in, haversack slung by a single strap over one shoulder, school tie tied at the skinny end to make a hard, nut-sized knot. He was a face. He had that hair. The boy/girl hair, parted in the middle, fading into bum-fluff at the ears and whisked up into a small bit of baloney at the back - back-combed into a high tuft or boll at the crown. He was sweet-faced. A true androgyne. And very sweet-natured. Cherubic, you would have to say, even allowing for the protuberant jug ears. Sweeno. He was a shy boy, as I remember him; neat and clean, with deep dimples when he smiled and a strawberry flush that constantly threatened to turn into a scalding, full-blown blush. Maybe that's why he started drinking. In his autobiographical Vietnam novel, The Things They Carried, Tim O'Brien claims that it wasn't being caught in crossfire or napalmed or blown apart that the "grunts" on the ground were most afraid of; what they were most afraid of was turning red in front of the other men in their company; they were scared of blushing.

The blurb for Barry MacSweeney's last collection, The Book of Demons, an account of how the demon drink chased and harried and finally (of course) caught him, says MacSweeney was an alcoholic from the age of 16. Many people doubt it. I doubt it. I knew him when he was 16. Not well (not at all, it now seems). I knew him when he was 17 and 18. But his first wife believes he was an alcoholic when she married him in 1968, when he was still only 20. Three years earlier, in a poem collected in his first book, The Boy From the Green Cabaret Tells of His Mother, he had written about "looking for these dark bottles/over the pelmet under the stairs/these green bottles in roomcorners/in the loft these peculiar places". A precocious premonition that his destiny was to be a plonkie.

MacSweeney wrote the cover copy for his last book himself: "Barry MacSweeney wrote his first poem at the age of seven and has been an alcoholic since he was 16 . . . His solitary hard drinking almost killed him, and after a series of life-threatening fits and convulsions, which ended with him on a life-support machine, he underwent rehabilitation through detoxification in several hospitals and an addiction clinic. He has now recovered." He wrote this in what was most likely a state of semi-stupor, the state in which he spent most of the last years of his life, still married to the sense of romantic mystery which allied him with the roster of flame-outs and fuck-ups and holy losers he had been fixated on from his youth.

"His notion of the artist was formed around a myth of exemplary failure and belated recognition," one of MacSweeney's obituarists, Andrew Crozier, wrote two weeks ago in the Guardian. "Rimbaud was an early model for this, others included Chatterton, Shelley, Van Gogh, Jim Morrison and Robert Johnson." A poet and literary academic, Crozier had known MacSweeney for 35 years. He first met him in a pub after a poetry reading in 1964 and remembers him as a moddy boy - a super-mod - carrying a biography of Van Gogh. "All that's missing is the parka," Crozier told MacSweeney, who was only trying to get a bit of bohemianism into his life. He reacted badly. Maybe that's why he started drinking.

He became a little bit beardy. Bushy sideboards and that sort of thing. Kind of wild hair. Big mutton-chop whiskers. But still a long way from what they used to call a beardy-weirdy. There used to be an expression used in the north-east: a face that looked like somebody had chopped sticks on it. Not Barry's face. Not Barry's face then, and - according to those who knew him, and in spite of taking up residence on "Cirrhosis Street, Wrecked Head Road", "living daily rim to mouth" - not Barry's face when he died. It's a long trip from "angel boyhood", as MacSweeney himself acknowledged, "to scarred bottledom". Yet, on the evidence of his friends, he remained - outwardly - remarkably unravaged, almost right up to the end.

His dapperness, it seems, never left him; his keen fastidiousness and his sense of style. Just before he published The Book of Demons in 1997, he tracked down a whisker on the map called Demon's Beck in Northumberland. He was living alone and in considerable squalor by this time, in a mess of bottles and takeaway cartons, usually nursing whatever injury had been caused by his latest fall. He had nasty falls. Toward the end he broke a lot of bones. Knee, ankle, shoulder, ribs - the final year he was seen by eight different hospitals for drink-related accidents. But one of the last pictures shows him in a long, dark overcoat over a black silk mohair suit, wearing a pair of shined-up black Florsheim shoes by the Beck, which turns out to be a rubble-clogged semi-sewer. "Lurking inside the shy Barry was another Barry," Jackie Litherland, his partner through the final years, says. "This was Barry the dandy. He had at least two people in his personality. He would retreat for weeks to what he called his "ravaged corner". His lair. It was like a den. A drinking den, really. But he was also a great dandy. Shoes immaculate, tie perfect, suit draped. He had a lot of style."

MacSweeney and I both had interviews with Thomson Newspapers in Newcastle when we were 16. I went back to school to do A-levels; he left to become a cub reporter on the Evening Chronicle. It was a move which, as luck would have it, brought him into everyday contact with a grizzled greybeard who had counted Ford Madox Ford, WB Yeats and Ezra Pound among his friends. By the early 60s, Basil Bunting had been working in obscurity as a subeditor on the Newcastle Chronicle for several years. His responsibilities included the daily tide table and the City column. Bunting was as old as the century, and his serious writing life seemed to be behind him in 1964. In fact, his reputation as England's major modernist poet was about to be revived by an 18-year-old self-confessed "work conchy" (conscientious objector) and "dole walla" called Tom Pickard, who had just rented a tower on the old city walls from Newcastle Corporation for 10 shillings a week and, with his wife Connie, was about to transform the cultural life of a region.

It is impossible to overstate the impact the Mordern Tower had on me as a booksniff sixth-former, and presumably on MacSweeney, who I regularly saw there as an aspiring poet. The beats came and things occasionally got riotous and dope was smoked. Instead of the usual adolescent maunderings and set texts, at Mordern Tower we were exposed to mad riffers and homosexuals and junkies; to Ed Dorn, Robert Creeley and Alex Trochhi; to Ferlinghetti, Gregory Corso, Ginsberg and other speakers of scary stuff we'd never heard before. Stuff that didn't scan or rhyme or do any of the things that our teachers at the grammar school told us it was meant to do. "Free verse", its visionary exaggerations jiving with a darkly "beat" personal style. It was for: the expression of immediate feeling and "visible truth"; the internal logic of sounds rather than imposed sense (letting it all hang out). It was against: careful, complex, ironic and well-finished work; the anecdotal and the small scale. I bought the donkey jacket; I wore the beard. But in MacSweeney's case, it changed his life. The isolation, the rejection, the gut-spilling, the torment and despair. He went the whole way.

The next time I saw him was in Hudson's student bookshop in Gosta Green in Birmingham. He was staring out at me from the vaguely psychedelic front cover of The Boy From The Green Cabaret Tells of His Mother, his first book. It was 1968 and he was 19 and a celebrity by virtue of having been put up for Oxford University's chair of poetry by his publisher. It was a scam, of course. A publicity stunt. But it was a less celebrity-fixated culture then, and MacSweeney wasn't wise to the ways of the world, and didn't see the train until it hit him. He got burned.

"He felt ridiculed," Jackie Litherland says. "They trashed him. He was just a kid. He found it very difficult to get published after that. He was seen as a 60s fashion victim. The talent didn't diminish, but his manuscripts were rejected."

"As an economic activity, poetry is marginal," Andrew Crozier says, "just as is, for example, hill farming. No one wishes to admit this." MacSweeney was a burn-out at 20. Surplus to requirements; edged out, marginalised; exiled from the mainstream. As it happened, this turned out to be not such a lonely place to be. At Mordern Tower it had been MacSweeney's good fortune to make the acquaintance of the Cambridge don and poet JH (Jeremy) Prynne. It was Prynne's belief that, freed from a unitary, closed-system, "great-tradition" view of culture, the margin could legitimately be seen as the centre. He was the eminence grise of the so-called Cambridge school of writers, which included Andrew Crozier and Peter Riley and, more indirectly, Peter Ackroyd and Iain Sinclair. Prynne is famous for the bloody intractability of his work; for what has been called its "almost mythic quality of luminous opacity". And he became MacSweeney's mentor.

Encouraged by Prynne in the early 70s, MacSweeney published a small-press appreciation of Thomas Chatterton that retrospectively, and probably inevitably, seems shot through with prescience. "Thomas Chatterton, the English romantic poet, was born in Bristol on November 20 1752, and swallowed arsenic 18 years later in London - starved and unrecognised," is Elegy For January's opening sentence. Later, apropos of apparently nothing, MacSweeney writes: "I think of the motorcyclist who does not attempt to avoid the head-on crash, but accelerates into his death."

For the remaining 30 plus years of his life, MacSweeney disappeared into the alternative universe of the little magazines; of fugitive publications and samizdat editions. He started a small imprint of his own, Blacksuede Boot Press, named for the Cuban-heeled boots Bob Dylan wore in the 60s. As a last resort, he would Roneo his poems and send them out to the hardcore of 20 people. "As long as they're out there. You always get the work out," he'd tell Jackie Litherland when she was having difficulty getting her own work published. More recently, he would hit the fax machine in the middle of the night, when he was on a bender and getting shitfaced and writing. His friend, Rick Caddel, co-director of the Basil Bunting poetry centre at the University of Durham, would arrive to find miles of fax paper being unravelled in the mornings by the secretaries. More of Barry's yes-I-am-drinking rants.

But did MacSweeney opt out of poetry's mainstream for ideological reasons, or was he shut out against his will, I wanted to know from Caddel when I went to see him. "There is a whole level of texts that define themselves by their unavailability," he said. "Editions of two or three-hundred or less. I think a lot of people prefer to be published this way. Certainly for Prynne for a long time it was an important point to control publication. Not to be seen to be in the same commodity market, as it were. Whether or not Barry deliberately chose to be published by the small presses, or whether he believed if he sent his work to Faber it would be rejected, I don't know. It is very dangerous to be part of that commoditised counter-culture, the way Tony Harrison is, say. I do know Barry agonised over sending The Book of Demons to Bloodaxe when the time came."

Ranter, MacSweeney's 1985 collection, had been turned down by Bloodaxe in Newcastle. He was devastated when The Tempers of Hazard, his selected poems, were pulped in the year of publication, after Rupert Murdoch acquired Paladin in 1993. He became reclusive and embittered. He disappeared into the bottle and lost his job as deputy editor of the Shields Gazette, where he had worked for eight years. It was around this time that his and Jackie Litherland's paths crossed again. They had originally met at National Union of Journalist conferences many years earlier when they were both attached to the NUJ. The person she encountered was not the Barry MacSweeney she remembered, but a shrinking, violently eczema'd figure, hiding under a baseball cap.

But he courted her, she says, "with a high style". When he was sober, they took trips to the country; he cooked, brewed exotic teas. When he was drinking, he disappeared to his lair in Newcastle and stayed there until he wanted to go sober again. It broke down into a pattern of roughly two months in each place. A dry period followed by the wet season. "I am the addict," as he wrote in one of his late poems, "strapping on his monumental thirst."

"The craving would return," Litherland says. "He'd become very violent. He had problems with anger. You can see it in the poems, which range from the most innocent things in his nature, right across to the most dark. But almost malicious. He'd reach a crescendo of craving. And then he'd just . . . do it."

MacSweeney had been in and out of hospitals and detox clinics for more than a year when, visiting him at his semi in Newcastle in June 1995, Litherland was witness to a catastrophic event. MacSweeney suffered a fit or convulsion in the course of which his head swelled terrifyingly and he vomited black foam and gouts of black blood. He had five more fits in quick succession in the hospital and was put on a life-support machine.

£10,000 from the Royal Literary Fund bought him a "cure" at a top drying-out clinic, and he went back to writing up his experiences in the series of bleak and terrifying - and occasionally jocular - poems that were to make up his last (but not his final) book. The Book of Demons is a work that MacSweeney apparently relished reading in public. It is a full-on rant through the language and, according to one witness, he was "completely transformed" when he performed these accounts of bodily trauma and pathetic abjection and breaking his head.

"I know it's a very middle-class way to describe it," Rick Caddel said, voicing some of my own reservations, "but I do wonder whether The Book of Demons celebrates the demons, or are they, as he claimed they were, being thrust away? I've got a very love/hate relationship with that book."

"The Book of Demons does celebrate drink," Jackie Litherland admits. "But it's written by an alcoholic. As an alcoholic, what you're fighting is your love of it; the fact that you adore it. That's the addiction. Alcoholics glory in the allure of drink. The demons only come when you want to give up. Because they want you to drink again. That's part of the attraction of the book for me."

Instead of being equal parts sober and blotto, the drinking binges started to extend until they entirely consumed MacSweeney's life. He started hallucinating wildly. He broke an ankle; a shoulder. He was forever topping-up and awash with drink. Burbling down the phone to his friends hour upon hour and falling over. He was never not drunk.

In 1995 he had published a set of poems which described his childhood relationship with a mute Northumbrian girl he taught to read and write. The poems in Pearl will stand alongside the best of their time and, together with the later Demons poems, represent the work by which MacSweeney is likely to be judged. But in the last year, friends say he had started to feel he had written himself out. He was drowning in drink and beginning to repeat himself.

Jackie Litherlan met him for dinner at Pani's, an Italian restaurant in the centre of Newcastle, on Friday May 5, just under four weeks ago. He brought her a rare Dylan bootleg - Dylan in Sydney, 1966 - which he told her he'd paid £100 for (he hadn't). He had been drinking, and he continued to drink. He collapsed when he stood up to go. But they knew him at Pani's, and they gave him half an hour to get himself together. After half and hour, he collapsed again. Jackie managed to get him into a taxi, which took him home.

The last person to talk to MacSweeney was Terry Kelly, a reporter on the South Shields Gazette who MacSweeney had worked alongside for years. He spoke to Kelly on the morning of Monday May 9 and then made a trip into Newcastle to buy a new Bob Dylan record that Kelly had mentioned on the phone. MacSweeney foresaw the manner of his own death: "One day choke on it, tongue/ jammed backwards down/ throat's clogged highway".

He failed to phone his mother to let her know he was still alive on the Tuesday morning. She discovered his body among the empties in the one room he used in his house. "Clink Eastwood", as he sometimes used to jokingly refer to himself.

• Memorial readings for Barry MacSweeney will be held in Newcastle on Friday June 16 at the Hatton Gallery, Newcastle University 2pm and 8pm at the Mordern Tower