Brendan at the Chelsea: The riotous new drama examines how drink inspired the great Irish playwright

Janet Behan's first attempt to put her uncle Brendan on the stage was a one-man show in which he talked about the various people and events in his life. She tried to be honest and fair, but a friend's criticism, she says, cut to the heart of what was wrong. "He told me, 'You've left out the most important character – the drink'." By contrast, Brendan at the Chelsea, in which Adrian Dunbar portrays the playwright, puts the drink centre stage, as Behan did all too often in his short (1923-1964), raucous life.

It takes place several months before he died, in his room at the Chelsea Hotel in New York, later known as the place where Nancy Spungen was murdered, but at that time dense with gentler artistic tenants and ghosts. Arthur Miller lived there while Brendan was a guest, and past residents or visitors included Mark Twain, Jack Kerouac, Tennessee Williams, Bob Dylan, Andy Warhol and Dylan Thomas, the last a disturbing augury.

Another Celtic author known for drink and riot, Thomas had a few years before left the Chelsea for the last time in an ambulance, to die in a nearby hospital of alcohol poisoning. Many feared Behan would end the same way, though he had, improbably, gone to this world of all-night parties and uncontrolled substances in order to dry out. The great black dancer Katherine Dunham, then staying in the hotel with her company, heard that he was too far gone to write, or even look after himself properly. She offered, if he moved there, to assign members of her troupe to take care of him and keep him off the sauce. For a while it worked.

The author of The Hostage and The Quare Fellow also needed a hotel that was no less bohemian than he. Before rock stars made lobby riots and pulverised furniture amusing, Behan's wildness had got him blacklisted by the Algonquin and other New York hotels used to writers who, if drunks, were more decorous ones. After abusing the staff and his credit in his last hotel, he had been shown the door by a proprietor who had good reason to fear worse – shortly before, in a Toronto hotel, Behan, when refused drink, had fought with the security man, and, when a second arrived, with both.

Behan's wife, Beatrice, who came over from Dublin to tell him she was pregnant for the first time in their 10-year marriage (he'd left the house without mentioning that he was off to New York), had long been locked into the role of caretaker and captive. The keynote of their marriage was struck on their honeymoon in France, when Behan rapidly spent the money for their trip on Pernod, and the newlyweds were reduced to bread and cheese and fleapits. He stayed on key right to the end, when he would go out on a three-day bender and return home before dawn with several prostitutes and pimps, for whom Beatrice had to get out of bed and serve tea.

She did not, however, marry unawares. Before Behan was famous as a writer, he was notorious as a drunk – it was said that, when he didn't have a bed for the night, he would wreck a pub – and, when he did become famous, it was as both. Invited to appear on Panorama, Behan responded to Malcolm Muggeridge's questions by taking his shoes off and having a snooze. He resurfaced to decry the time wasted watching television, when a viewer might instead "be making love, walking the dog, or having a pint – or even all three at once".

On American television, equally lubricated, he announced jauntily that the foundation stone of the Protestant church was "the bollocks of Henry VIII". Janet Behan met Brendan only a few times – her family, headed by his playwright brother Brian, lived in London, and she was 10 when he died – but as a child was well aware of his reputation. "I was always being asked, 'Is your uncle a genius, or just an alcoholic?'."

The problem was that even those who knew Behan only as a drinking companion were seduced to the former view. Behan could be violent when he had had a few, enough to get him blacklisted from numerous pubs, and even from the St Patrick's Day parade in New York, but he was also, as he called himself, "the best banned in the land" – a fount of witticisms, imitations and satirical songs that he made up on the spur of the moment.

Those who tried to keep him sober were always outnumbered by those who wanted him to provide the evening's entertainment, even though it might cost him his life: when drunk, he would forget to take the insulin that controlled his diabetes. Indeed, he once collapsed in the street, in a diabetic coma, though, fortunately, in front of the house of one of the most eminent doctors in Dublin.

Why did Behan drink so much? Even a brief look at his life and milieu makes one ask, rather, why wouldn't he? The first time Janet Behan visited Dublin as a teenager, she says, "I took a look around the pub and thought, 'My God, they're all alcoholics.'" Drinking was an unquestioned way of dulling the pain of existence for the Irish, living with the aftermath of centuries of brutal exploitation, a country that suffered the social equivalent of child abuse. Behan's father would regularly come home from his painting job, having stopped off on the way, and fall on the floor. His mother, whom he adored, was affectionate and jolly, but not one to challenge the national pastime, only shaking her head when Behan's grandmother took him on pub crawls before he was even 10 years old.

The poverty and uncertainty of Behan's childhood, during the Depression, was such that, as Janet's father Brian recalled, their mother once had to empty a cushion she had stuffed with oats to make porridge for her six children. At such a time, Behan said, "To get enough to eat was regarded as an achievement. To get drunk was a victory". The lack of money for drink, however, imposed a limit that no longer existed when Behan became a successful playwright. Suddenly there was enough cash for him to drink his fill, and to be seen celebrating his victory over poverty and obscurity.

The years Behan spent in borstal and prison for his IRA activities (the former became the basis for his novel Borstal Boy) also fed his craving for merriment to make up for what he had missed. Eamonn Martin, whose father's life Behan had saved, at 13, by confronting a Fascist mob with a loaded pistol, said that the welcome-home parties after his second spell in prison were so wonderful that "I think he decided to adopt them as a way of life."

But the fame that gave Behan the means to drink also gave him another reason to do so. His three serious works had their roots in his own suffering but also in the rich brew of songs and stories that had coloured his world from infancy. With the hardship removed, as well as the intimacy with the poor, who need ballads and legends as much as bread, Behan was deracinated and adrift.

Cut off from his reality, he used drink for refuge, making the noise of an empty vessel. To remind people that the man who wrote the plays still existed, Behan would go to the theatre drunk, sing, heckle, and try to mount the stage. When caterwauling in pubs wasn't loud enough for him, he broke their windows. Small wonder that, at the end of his life, he referred repeatedly to the character in The Little Prince who, asked why he drinks, says, "Because I am ashamed", and, asked of what, says, "Drinking."

The reason that is nearest the bone may be found in Behan's bitter description of Dublin as a city of "familiarity without friendliness, loneliness without solitude". His greatest nightmare was being left alone – the solitary confinement in prison, he said, nearly drove him mad – and alcohol was company in itself.

For all its treachery to him, the most important character in Behan's life was, indeed, "the drink", a friend that, however degraded he became, would never leave him. "It's better to be fighting than to be lonely," he said, but the sparring partner he could never abandon led him to the loneliest place of all.

'Brendan at the Chelsea' runs to 3 February, Riverside Studios, Crisp Road, London W6 (020-8237 1111; www.riversidestudios.co.uk)