Director: Michael Winterbottom
Cast: Rosie Fellner, Marta Barrio, Steve Coogan, Rob Brydon

"Rob can't read poetry in his own voice because he lacks conviction."

That's Steve Coogan, playing Steve Coogan, talking about Rob Brydon, playing Rob Brydon. It's par for the course for The Trip to Italy, the follow-up to 2010's The Trip, which sees the pair team up again to journey around Italy, eating at restaurants, drinking wine and seeing who can do the best Michael Caine impression. This time, the show aims higher: the repertoire extends to Christian Bale and Tom Hardy's Bane as well.

Two middle-aged actors sitting around getting drunk? Michael Winterbottom's film (edited down from the six-part TV series) should come across as insufferably smug, but plays its hand far too subtly for that; Coogan and Brydon send themselves up without mercy, their fictionalised personas cut so close to the bone that you swear they're not fictional at all. "I'm an affable man, but not as affable as I am on-screen," explains fictional Rob, dissecting factual Rob with a straight face. Coogan nods. "I'm affable," Rob insists, aggressively. "I'm affable!"

It's rare that they don't talk about themselves; another stroke of nuanced self-mockery. "There's not much difference between Byron and Brydon. Only a 'd'," observes Rob at another hotel. Steve scoffs, while eyeing up a receptionist. On this vacation, though, the womanising roles are reversed: where Steve was (believably) the one playing away from home in the first season, here Rob is more unsettled in his marriage. He soon finds himself in the arms of their sailing guide, Lucy (the excellent Rosie Fellner, last seen in Two Jacks), while Coogan has to face the return of a familiar face: photographer Yolanda (Marta Barrio).

That's as near to a narrative arc as Winterbottom's gently structured holiday gets; the seemingly perpetual male tour of mid-life crisis, infidelity, guilt and Michael Caine impressions. Accompanied by opera as they float away from the Italian Riviera, the pair seem more preoccupied with their shelf life than ever. Like the Romantic poets they invoke - in the style of Anthony Hopkins, Hugh Grant, Ronnie Corbett and more - how will they be remembered in 200 years time? A visit to Pompeii sees Rob reprise his "little man in a box" routine with a corpse, a moment full of unexpected pathos as much as silly voices. Like all the best inebriated conversations with your best friend, there are moments when their prattling seems to reach philosophical heights - maturity, via a long, immature detour.

All of this wouldn't work, though, without two brave performers. Undermining and celebrating each other repeatedly, they poke at their co-star's shortcomings with the kind of familiarity that can only - and, indeed, does - come from a genuine off-screen friendship. The stunning scenery, shot with a relaxed eye by Winterbottom, and mouth-watering cutaways to kitchen staff preparing dinner, are beautiful - but the thing to savour is the relationship between the couple taking it all in.

For that reason, the BBC TV series is superior to the film version, cut down to sell for international audiences and shown at Sundance London this weekend; there is more time to soak up their seemingly natural company, which the movie lounges in for the first three episodes, then skips quickly through the rest. To say one is better than the other, though, is like ranking fine wines - or Steve and Rob's Michael Caine impressions.

Two middle-aged actors sitting around getting trollied shouldn't be entertaining. But in fact, you want as much of it as you can get - preferably, in small half-hour courses. Not just because their impressions are hysterical - they are - but because of what they reveal about the men. For a pair so concerned with deconstructing their own appearance and identity, both fictionalised and factual, it's apt that they spend most of the time communicating through the medium of other people - showcasing their comedic talents as well as their insecurity.

"Rob can't read poetry in his own voice because he lacks conviction," stabs Coogan. It hits home. Impersonations of impersonations of people doing impersonations, that reliance upon pretending to be something they're not gives The Trip to Italy a conviction as breathtaking as anything the Amalfi coast has to offer. Of course, that could just be the alcohol talking.