MICHAEL Winterbottom’s irreverent take on Laurence Sterne’s unreadable classic, The Life and Opinions of Tristram Shandy, Gentleman, is the funniest film of the festival by far.

It’s a savoury piece of cheek: a rude, ruddy satire about the film business, and an awesome tour de force by Steve Coogan. The comedian plays four vastly similar egos: Shandy, his father, Walter, Sterne, the writer, and of course Coogan himself. Apart from changing his wigs, he makes no effort to distinguish his characters. They are as prickly as porcupines and as thin-skinned as balloons.

The film flips between the 18th century and the squabbling film-makers who are attempting to shoot this impossible novel on a shoestring.

Coogan and his co-star, Rob Brydon (Uncle Toby), bicker endlessly about their billing, the height of their shoes, and the size of their parts.

“I should dominate at all times,” Coogan announces with a pompous whine.

Brydon responds with perfect Alan Partridge impersonations that drive his rival mad. At the end of one typical day on set Coogan tries to snog his personal assistant; a tabloid journalist chases him about a sex scandal; his wife (Kelly Macdonald) arrives with their squalling six-month-old baby; the financiers threaten to pull the plug on the film, and his director (Jeremy Northam) ignores his star’s efforts to enlarge his role.

You can’t blink without missing something fiendishly clever, or fabulously embarrassing. Many an auteur has tried to play this game of mixing fiction with layers of “reality” and come wretchedly unstuck. Winterbottom and his terrific cast make this post-modern lark look as natural as breathing.

The shameless, improvising pleasure is Coogan. He simply can’t help his egomania even when he’s not in the scene. An eight-year-old actor, playing the young Tristram, has his penis trapped by a sash window when he urinates into the courtyard. “This is the best of a bad bunch,” Coogan moans about the boy’s performance. No one takes the blindest bit of notice. Frankly, no one seems to care what he thinks.

The irony is how seriously Coogan takes his art. At one point the grumpy actor is suspended, naked, in a giant pink plastic stomach about to deliver his Tristram’s birth scene.

“You want more realism?” Coogan splutters at the assistant director. “I’m a grown man upside down talking to you from a womb.” In his hotel room he studiously ignores his wife and has a nightmare about Rob Brydon’s new romantic scenes with Gillian Anderson as Widow Wadman.

It’s hard to imagine that this farce has been fashioned by a director who made his biggest splashes with harrowing pictures about the Third World Diaspora. In terms of broad and knowing entertainment, there’s precious little out there to top this vintage bull.