In an age when creative original scripts are in short supply, the film industry has become increasingly reliant on published works of fiction for "inspiration." To the chagrin of many executives, however, most books' textual richness and quirky charms don't translate easily onto film.

Books can run the gamut from the filmable to the unfilmable. Those that offer up a simple, linear narrative and eschew an overemphasis on interiority can make great films in the right hands. Those that spend more time in psychological and symbolic spaces tend to give filmmakers a tougher challenge. The valiant directors who opt to take on the latter category are often forced to radically re-imagine their source material (think of David Cronenberg's adaptation of William Burroughs's Naked Lunch); those unable to give such books new life, however, are doomed to join Alan Rudolph's disastrous 1999 adaptation of Kurt Vonnegut's Breakfast of Champions, now ranked high among the most hated films of all time.

For these reasons, I was particularly interested to see what the chameleon-like British director Michael Winterbottom would do with the ultimate unfilmable book: Laurence Sterne's epic and obese The Life and Opinions of Tristram Shandy, Gentleman.

Tristram Shandy is a very silly book-it's the story of what happens on the way to its own telling. Tristram Shandy, the befuddled narrator and would-be-protagonist, sets out to write his own life story. The problem, he soon finds, is that there is quite a bit to explain; from his uncle's unfortunate "accident" at the Siege of Namur to the invention of forceps. By the midway point of his 500-odd-page tome, Tristram still hasn't got around to recounting his own birth. The novel is equally riotous and maddening; an amorphous work that delights in Falstaffian excess and thumbs its nose at any pretence to linearity. As I said before, it's unfilmable.

Of course, they said the same thing of Cervantes's Don Quixote. In 2000, Terry Gilliam set out to make The Man Who Killed Don Quixote, an adaptation of Cervantes's masterwork that would have seen a modern-day marketing executive (played by Johnny Depp) stumble into Don Quixote's world. The ambitious film was beset by so many difficulties that it ultimately had to be abandoned-luckily, documentary filmmakers Keith Fulton and Louis Pepe were there to record Gilliam's failed odyssey. As their film Lost in La Mancha ultimately proved, a possessed director brazenly defying the possible in his quest to film the unfilmable communicated Quixote's themes far better than Gilliam's creative adaptation ever could have. In Fulton and Pepe's documentary, filmmaking became a potent modern metaphor for the scope of human dreams and the depth of human endurance in the face of stark reality.

Inspired by Lost in La Mancha, as well as by the postmodern mastery of Charlie Kauffman's Adaptation, British director Michael Winterbottom has re-imagined Sterne's novel in a way that does justice to its inventiveness and keen sense of play. The film's title announces that, like its source material, it is a "cock-and-bull story"-what the Dictionary of the Vulgar Tongue refers to as "a roundabout story, without head or tail, i.e. beginning or ending." Winterbottom's movie defies the boundaries between art and reality, absorbing and playing with the real lives of its actors while refusing the confines of strict narrative form.

This, of course, guarantees that the film will rub a lot of people the wrong way. The New Yorker's David Denby recently panned Tristram Shandy: A Cock and Bull Story. "One trouble with the current vogue for meta-cinema," Denby writes, "is that its practitioners, such as Winterbottom and Charlie Kauffman, underestimate the extraordinary difficulty of telling a story straight." While I doubt that either Winterbottom or Kauffman would deny the talents of Noah Baumbach, Larry McMurtry or Diana Ossana, Denby clearly underestimates how difficult it is to tell a story sideways and do it well.

Winterbottom's movie works because it does to film production what Sterne's book did to the emerging form of the novel in the 1760s. Winterbottom turns the film medium inside out, presenting itself as a movie that wants to get made but is constantly fighting for time, funds and inspiration. After shooting the opening of the novel as straight as can be expected, the director (Jeremy Northam, playing Winterbottom) yells, "Cut!" and the brimming backstage life of the Tristram Shandy set swallows up the remainder of the movie.

At the centre of it all are British comedians Steve Coogan (Tony Wilson in Winterbottom's 24 Hour Party People and the genius behind comic creation Alan Partridge) and Rob Brydon (who played Keith Barrett on the BBC's Marion and Geoff). The two veteran comics duel throughout. Largely improvised scenes see the duo bickering over everything from who can do the better Pacino impression to the colour of Rob's teeth.

Coogan offers up a note-perfect parody of his own public persona-the preening, sex-crazed star. He lusts after the PA, demands extra heel so he can tower over Brydon (in case anyone should forget who has top billing) and gives celebrity interviews on the wonders of family life in order to cover up a lap dance with a stripper. Every time Coogan is about to steal a moment with his wife (if only to quell the rumours circulating around the set that he has lost his libido), he's called away to discuss the direction of the film; and when he finally does secure a moment, Coogan discovers that Rob may have more screen time than him. Only then, with his wife panting in bed across the room, does the comedian bother to read the novel.

Like Charlie Kauffman/Spike Jonze's Adaptation, Tristram Shandy: A Cock-and-Bull Story is about the process of transposing a book's content onto film. But given that Sterne's novel was about the difficulties of transposing a life-indeed, the complexity of existence itself-onto the page, Winterbottom's effort seems rather faithful. Of course, to those who haven't read the book, none of this really matters. To them, all that matters is if Winterbottom's film is funny. And it is.

Midway through the adaptation of Tristram Shandy, the company reaches an impasse. Lacking the funds to properly execute a battle scene and debating which plot elements to drag from the novel into the ever-evolving script, the team tries to remember why they wanted to make the film in the first place. "Because it's funny," the director suggests after a prolonged silence, "Isn't that enough?"

The answer, of course, is yes. Sterne's novel works and survives because, along with being ahead of its time ("Postmodern before there was any modern to be post of," Coogan declares at one point in the film), it is uproariously funny. Winterbottom's film captures some of the more hilarious moments from the book while incorporating extended stretches of improvised banter that, unlike so much contemporary American comedy, remains literate, character-based and deeply human.

Winterbottom's film is hardly breaking new ground. The behind-the-scenes mockumentary has been done a thousand times, from The Larry Sanders Show to Ken Finkleman's The Newsroom. To many, meta-cinema and the media industry's seemingly endless desire to parody itself is growing tired. But for a moment, why not abandon the discussion around whether Charlie Kauffman has invited years of lazy cinematic adaptation? Sure, we may soon see a third-rate filmmaker making a cheap film about the cast of Surreal Life filming The Brothers Karamazov-and on that day, I'll weep for cinema too-but in Tristram Shandy: A Cock-and-Bull Story, Michael Winterbottom has given us an inventive adaptation, and one that works. The film taps into the heart of Sterne's book and wrenches its themes and questions into the twenty-first century in a hilarious and consistently entertaining way.

A toast! To sideways storytelling, done well.