An evening in the theatre that begins at 6.30 and ends at 11.45 doesn't immediately make the heart leap. Five and a quarter hours - surely a bit of editing wouldn't go amiss. Or so I imagined before I saw Cloudstreet in London, on the way to its Dublin Theatre Festival slot.

Cloudstreet is adapted from the long sprawling novel by Tim Winton, which has become an Australian classic since it was published in 1991. It won numerous awards in its original incarnation and Winton's later novel The Riders, set in Ireland and Europe was shortlisted for the Booker Prize in 1995.

However, taking a much-loved novel and adapting it for the stage is a risky undertaking, particularly a novel that is richly poetic in language and in form, hovers a good few feet above naturalism.

No 1 Cloudstreet is a rambling, ramshackle house lived in by two disparate families, the feckless and reckless Pickles who inherited it from a relative, and the hardworking godfearing Lambs who are refugees from a terrible family tragedy. If the families represent the two sides of the white Australian heritage, the house could be said to be a metaphor for Australia itself, haunted by the ghosts of aboriginal orphans and white guardians who once lived there.

Tim Winton himself was not involved in the adaptation, but Nick Enright and Justin Monjo have been remarkably faithful to the original, not only to the crackling fair-dinkum dialogue, lifted pretty much straight from the page, but also to Winton's poetic narrative, spoken directly to audience either by the characters it concerns, or the shadowy aboriginal narrator.

At the heart of the novel and the play is Fish Lamb, the brightest of the five Lamb children who as the result of an accident when he is nine - a superbly staged opening to the play - is brain damaged and becomes, in effect, an idiot savant. Around him the other characters circle, his elder brother Quick, guilt-ridden by his failure to prevent the accident, his mother Oriel a thin, prim woman who's lost her faith, his father, Lester, an ever-smiling dogged, good man.

On the other side of the partition are their landlords; the promiscuous Dolly, ebullient gambler Sam and their long-suffering daughter Rose, who discovers in Fish someone more vulnerable than her.

The ring-fenced intimacy experienced by close-living neighbours has well-reconised dramatic potential, most obviously through television soaps.

But where Neighbours gives us a banal version of Australian life observed through the bottom of a plastic beer mug, Cloudstreet explores the deeper, elemental essence of the Australian experience: the love-hate relationship with the land, its abundance and its unforgiving harshness; the shared guilt of an unclear past, together with a sense of unnamed shame.

The action spans 20 years from the outbreak of war to the late 1950s, ending with the birth of a child the year Tim Winton was born. Cloudstreet was written in some measure, Winton says, to reclaim his personal past. "We're going to have nothing to pass on to our children but the sky," he told Neil Armfield, the director as they toured the Swan River region of south western material where Winton grew up and where Cloudstreet is set. "No sense of place or the growing, inherited sense of culture that gathers around a city or a particular physical environment. The memory is being lost, and without that memory there is ultimately no civilisation."

Perth is isolated from the rest of Australia, and the world, by sea, land and sky and these elements form the physical frame for the production in which resourcefulness takes the place of money.

I first read Cloudstreet when I returned from Australia earlier this year and it touched and moved me in its exploration of the nature of love, friendship and pain in a way that my time in Australia itself had not. I thought it an unfathomable place, with Australians proud of the future but dismissive, if not actually silent about the past.

Questions about an individual's antecedents, or even more general historical discussion, proved an easy way to end an otherwise friendly conversation, ditto anything to do with aboriginals. Those few people interested in preventing the destruction of 19th century European heritage and restoring what has been preserved are hard put to raise either money or interest.

Towns turn their faces away from the land and face inward towards each other, in a wagon-train mentality. Only in the last few years has Sydney begun to exploit the harbour as somewhere to sit and watch the world go by.

If the novel is clearly about a lost Australia, the play is also an expression of contemporary Australian cultural vitality. The Sydney-based Company B Belvoir, who first staged Cloustreet at the Sydney and Perth Fesivals in 1998, itself grew out of action to save Sydney's Nimrod Theatre from demolition in 1984.

The company is an example of live theatre at its most powerful and inclusive, where actors, director, writers, musicians and designers combine talents to present a theatrical experience of extraordinary quality, not least through the performances of the 14 actors who take on a total of 35-odd parts.

The night I saw the show at London's Riverside Theatre, an accident to one of the cast - involving a trip to casualty and a stiched up knee - led to a delay of an hour and a half in starting the second act, and by the time the show ended - to a standing ovation - it was gone one o'clock in the morning. Over six hours since we'd all started out, yet there was with no sense of relief, but rather one of sadness that a shared experience of such emotional power had come to an end.

Cloudstreet runs at the SFX City Theatre on October 8th, 12th, 13th at 5.30 p.m.; and on October 9th and 10th at 4.30 p.m.