The world is always present in the films of Sally Potter, waiting outside, guiding and influencing the lives of people within her specific and intense gaze. And so it is in “The Party,” her confident and economical chamber piece, a full and satisfying experience that clocks in at only 71 minutes.

The occasion for celebration is the election of Janet (Kristin Scott Thomas), who has become a minister of Parliament and the shadow minister of health. That is, she will be the health minister if her political party comes into power. As Thomas can often seem, she is a study in competence, integrating visitors and congratulatory phone calls into a steady stream, while chopping onions and preparing dinner.

But something doesn’t feel right. Although the party should be a happy one, an aura of defeat and disappointment hangs over the house. Her closest friends — played by Patricia Clarkson and Cherry Jones — can’t conceal a certain ambivalence about Janet’s elevation. Meanwhile, Janet’s husband, Bill (Timothy Spall) sits in the living room with a zombie-like expression, as if stricken by the realization that he’s about to become Margaret Thatcher’s husband.

As you can tell already, Potter (“Orlando,” “Ginger & Rosa) has attracted a strong cast, and that strength extends to all the roles. Emily Mortimer plays Jones’ pregnant lover, who announces triumphantly that she is having triplets — and expects this to be greeted as good news. Cillian Murphy is an Irish investment banker, who looks swell in his expensive suit, but keeps running into the bathroom to snort cocaine. And best of all, there’s Bruno Ganz as Gottfried, looking as loony-radiant as Timothy Leary, as he spouts new age bromides.

Shot in a glossy, appealing black-and-white and filmed in a single location, ”The Party“ generates a pressure cooker atmosphere. The characters’ clashing grievances bespeak an underlying middle-aged and late-middle-age despair, the sense of people carrying on despite an uneasy sense that there is no point. Considering that the characters are all professional altruists, this encroaching nihilism suggests a larger significance. There’s something wrong, not just in the room, but outside.

This feeling is not easy to explain or define. If it were, there might have been no need for Potter to express it through art. But its overall sense is that something is giving way, that the civility with which these people live their lives and the reality that they have assumed are simply not adequate to the challenges outside their doorstep. The world is caving in, and the strain of pretending otherwise is starting to show.

MOVIE REVIEW

“The Party”

Grade: B

Starring Kristin Scott Thomas, Timothy Spall and Patricia Clarkson. Directed by Sally Potter.

Rated R for language and drug use. Check listings for theaters. 1 hour, 11 minutes.

Bottom line: A satisfying film with a strong cast