Brendan at the Chelsea

'Sweary, sweaty and stocky' Adrian Dunbar turns in a compelling performance

By his own admission, Brendan Behan had a horror of being ordinary, of being – as he put it, with characteristically whimsical self-obsession – 'just an ordinary human Behan'.

He was in love with the idea of greatness, with living the life of a chaotic, decadent, emotionally-charged artist, flying high above the ordinary masses who spend their humdrum lives clipping their hedges and polishing their cars.

But when we meet Brendan Behan in the Chelsea, shacked up in squalor at the legendary bohemian hotel in New York, his wings are withering fast, and he's paying a bitter price for his excesses, his desperate need to 'grab at life'.

Behan's Broadway play, The Hostage, is a success, but he is a mess – embroiled in a complicated relationship with his mistress and child, warring with his wife Beatrice, behind with his deadlines.

Unable to hold a pen any more because of the advanced effects of his alcoholism, we see Behan in a downward spiral of self-destruction. He is an overgrown, petulant, selfish child who has to have his own cup supported to his lips and is noisily resistant to his friends' attempts to help him save himself.

This being Brendan Behan, though, he's still capable of flashes of mordant, earthy wit. Reacting to a positive review of The Hostage he says 'sure they'd praise me balls if only I hung them high enough.' He proclaims New York to be 'a most city-like city – the place where you're least likely to get a bite from a wild sheep'.

He condemns his friend George for being a 'sipper' of alcoholic drinks – the worst insult, presumably, in the Behan inventory. It's like life, it makes it last longer if you sip, protests George. 'Makes it feel longer too,' says Behan, which tells you everything you need to know about the man.

Spending a couple of hours in the company of a maudlin alcoholic isn't the most appetising of prospects, even when it's Brendan Behan. But Adrian Dunbar (who also directs) is so compelling, so absorbing as Behan, the minutes fly by.

Yes, the writing by Janet Behan, the writer's great-niece is good, and the supporting characters – especially Beatrice (Pauline Hutton) and Lianne, Behan's long-suffering assistant (Renee Castle) – are fine, competent actors. But that's the difference: the others may be acting, but it's as though Dunbar actually inhabits Behan's skin.

He is, of course, suitably sweary, sweaty and stocky, as you would expect. More than that, he channels Behan's irascible, charming, infuriating spirit, right down to the way he mutters and groans to himself while alone and nursing a hangover. Adrian Dunbar is mesmerising, and that's what makes this play sing.

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