A Prairie Home Companion (PG)

Robert Altman, who died in November aged 81, lived to be an old man but he had the rare good fortune not to become a grand old man. He was too mercurial, experimental, facetious to acquire the respectability that can embalm artists while they're still active. There's no solemnity to his final film A Prairie Home Companion. Not what you'd normally think of as a great director's farewell, this is more a cheerfully casual that's-all-he-wrote from a testy old cove who had the foresight to organise his own rowdy wake, complete with band, booze and dirty jokes.

You're glad Altman lived to make this his exit note, rather than sign out on any of his foggy, half-achieved films of recent years. Even the admirable Gosford Park wouldn't have been quite the same: it's too polished and complete an object. It's the bustling raggedness, minor-key bluesy humour, and downright indifference to filmic protocol that make A Prairie Home Companion such a perfect farewell.

As in much of his best work, Altman starts with someone else's material and infuses it with his own rhythms: this film floats to a lazy, seemingly extemporised choreography that is Altman's umistakable signature. The film is based on the long-running American radio show of the same name, fronted by author Garrison Keillor, who has also written the script. Keillor and Altman give us a fictionalised staging of the show, taped as in real life before an audience at the Fitzgerald Theater, St Paul, Minnesota. Keillor, or his lookalike "GK", presides over the bill with an owlish solemnity reminiscent of Kenneth Horne, dispensing lugubrious corncob wit (on Minnesotans: "We are a dark people: people who believe it could be worse, and are waiting for it to be worse"), and crooning along with the vocal talent. Featured acts are cowboy duo Dusty and Lefty (Woody Harrelson and John C Reilly), specialists in punning repartee and apocryphal yee-ha ditties ("I'll Give You My Moonshine If You Show Me Your Jugs") and harmonising sisters Yolanda and Rhonda Johnson (Meryl Streep and Lily Tomlin), superannuated sweethearts of the rodeo.

The onstage proceedings are brisk and tuneful, if occasionally verging on the twee. But the real fun goes on backstage, as the acts prepare, exasperate the radio staff (notably Maya Rudolph's long-suffering production manager), reminisce about shows gone by, and generally talk over each other in a very pronounced example of the famous Altman overlapping dialogue (he seems almost to be sending up his own trademark, but in a way that sounds perfectly natural and casual).

You'll miss much of the dialogue, but what the actors say matters less than the slippery grace with which their voices bump into, glide over and fold round each other. The balancing act between chaos and order, flipness and professional seriousness, is the whole game, and it's there too in the elegant choreography of the camera movement. Altman and cinematographer Ed Lachman go out of their way to set challenges for themselves, to prevent this ostensibly theatrical film from becoming static: the camera follows characters stalking around the fringes of the stage, as they watch the action, spy on each other, make nuisances of themselves. Kevin Kline's inept Forties-style gumshoe Guy Noir executes almost-elegant pratfalls around the venue as he trails Virginia Madsen's trenchcoated femme fatale - quite literally fatale, as it happens - who's forever winding unseen in and out of the wings.

But behind the larkiness, a more sombre mood is in the air, for this is a story about endings. We're watching the very final episode of GK's show, which in this fictional universe is being axed by the network; the axeman himself, played by a formidably sour-chopped Tommy Lee Jones, is expected any moment. One character actually dies in the course of the evening, prompting the knowing line that leaves you in no doubt about what was on Altman's mind when making the film: "The death of an old man is not a tragedy."

And indeed it's not: it's cause for lamentation, fond remembrance and another round of beer. Not long after the aforementioned death, Dusty and Lefty launch into their show-stopping number "Bad Jokes", a shameless and priceless litany of hoary double entendres - as if to say that death itself may be a bad joke, but there's no reason not to laugh. The one person who takes death too seriously is Yolanda's daughter Lola (Lindsay Lohan), an earnest kid with a notebook full of songs about hanging yourself on an extension cord; even she, however, has to lighten up and strike up a tune when things get real.

Some elements of the film's flip Americana might rankle slightly. Certainly, there's a hovering whiff of gingham, especially around Meryl Streep's dewy-eyed matron, a walking miasma of pastel and sepia, but then she has Lily Tomlin as a cranky acidic foil. But while Garrison Keillor might be a sentimentalist, Altman sure as hell isn't: A Prairie Home Companion is neither too sweet nor too serious. It's a minor film, for sure, but that's Altman's style. While some film-makers might have departed by leaving a sombre mausoleum for themselves, Altman prefers to erect a ramshackle, over-populated, vaudeville theatre where everyone keeps talking at once and there's always another entertainment to follow. It's a perfect miniature of his own oeuvre.

j.romney@independent.co.uk