Potiche, François Ozon, 102 mins (15)

Deneuve is reunited with Depardieu in a deliciously retro boardroom farce

Le style, c'est le film – it's a principle that François Ozon knows well.

And it explains why a somewhat dog-eared French stage farce from 1980, shot to resemble a TV sitcom of the period, makes for an exhilaratingly funny film. The title Potiche translates as something like "trophy wife", but the fact that it sounds like "pastiche" sums up the particular flavour of Ozon's film, which manages to be at once retro and very of-the-moment, at once impeccably sophisticated and as cheesy as a job lot of Roquefort straight off the back of a camion.

There's genuinely no knowing what you're going to get next from the prolific Ozon – downbeat dramas, costume follies, psycho-thrillers, he's done them all. But Ozon's taste for camp is to the fore in Potiche, which does for French boulevard comedy (the British equivalent might be a Brian Rix or Ray Cooney farce) roughly what Todd Haynes's Far From Heaven did for the 1950s melodramas of Douglas Sirk. In other words, it takes a period form and at once feminises it and "queers" it to modern sexual-politics specifications. This may sound like a sobering ration of cinematic vegetables, but Potiche is a hoot.

Set in the late 1970s, the film is about moneyed bourgeoise Suzanne (Catherine Deneuve), the decidedly unfeminist wife of Robert (Fabrice Luchini), who now runs the umbrella factory founded by Suzanne's father. The consummate potiche or accessory, Suzanne spends her days fussing around the couple's chintzy home and writing terrible doggerel. When Robert's angry workforce rises up against his unreconstructed iron-fist capitalism, Suzanne finds herself heading negotiations. That means striking a deal with communist MP Maurice (Gérard Depardieu), an old-school militant – and an old flame of Suzanne.

The flame is reignited, not least on a disco floor where Depardieu and Deneuve strut their stuff – if strutting is the term for such a ceremonial and oddly cautious set of moves from these two rather solid keystones of French cinema. Meanwhile, Suzanne takes over the factory, instituting a new reign of enlightened creativity with her son Laurent (Jérémie Renier) – an artistic boy whose references to a never-seen fiancée shouldn't blind us to the messages sent by his increasingly flamboyant body language and dress sense.

The material Ozon is working with here – his script is "freely adapted" from the play by Barillet and Grédy – is broad, creaky, and built on stereotypes and their somewhat obvious comic inversion. Robert, fated to be comically emasculated, is a curmudgeonly tyrant who treats everyone like his minions, including his mistress – played very funnily by Karin Viard as that very 1970s oxymoron, the buttoned-up sexpot. Suzanne blithely accepts her place as the little lady at home, until it comes to the crunch and the sexual and social roles are reversed – with consequences that might have been straightforwardly hilarious to a French farce-going audience in 1980 but that now acquire a patina of retrospective irony.

Ozon invites us to gasp at the cartoonishness of the period humour, notably when Suzanne sweet-talks a committee of strikers, depicted as unkempt and mad-eyed bolshy. But by making us laugh at the archaic humour that would have tickled a mainstream middle-class audience 30 years ago, Ozon shows that from this apparently outmoded material, insight is still to be had. It's much the same double-edged perspective on which Mad Men is constructed – reminding us how wildly different the recent past was, and yet suggesting that deep down, our own attitudes haven't changed as much as we like to think.

Ozon manipulates style brilliantly, making every shot, every line, every gesture perfectly tuned to the form he's recreating – Viard's prim shrugs, Luchini's exasperated tics are a magnificently calibrated ballet. The casting itself is witty. Luchini is extremely funny as the boorish Robert – partly because the actor is best known for playing exquisitely mannered highbrows, notably in Eric Rohmer's films. But Ozon's masterstroke is to reunite Deneuve and Depardieu, in their seventh screen pairing. He even indulges a fan's fantasy about how it might have been if they had co-starred before they actually did. They first shared the screen in 1980, but in a flashback to Suzanne and Maurice's youthful fling, Ozon uses lookalikes to imagine 1970s-vintage Depardieu getting it on with Deneuve in her 1960s prime.

Depardieu plays the old-school leftie as a humbled scrapper, but there's an enormous poignancy to Suzanne's rekindling of both Maurice's political and romantic drives. On top form for the second time in a month, two weeks after road comedy Mammuth, Depardieu looms with droll tenderness, but he has the delicacy to recognise that the film is absolutely Deneuve's show.

And it certainly is that. Despite her perennial renown as French cinema's cut-glass queen, Deneuve reminds us here that she has a sense of humour – she not only lets her hair down but sends up her stateliness with magnificent brio. The film is hers from the very start, when Suzanne goes for her morning jog, stopping off to pen her poems to the birds and bunnies, like Snow White in her matronage. Somehow the sight of the ever-lofty Deneuve in a red tracksuit is inherently funny, and the star knows it. I can't think when we've seen a national monument having so much fun.

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