A strong theme informs the Second World War drama Suite Française, concerning the way that society's class structure can become even more heightened during wartime; rather than people "coming together" in adversity, here the burghers of a rural French town pose as much threat to each other as the Germans do.

This is material enough for a drama. Unfortunately, the focus of the film is an increasingly soporific romance. And the whole is diluted by the customary presumption of filmmakers that it's somehow fine to cast English-speaking actors as Europeans; the result not only feels inauthentic, but totally wrong. And what might have been a fabulous film is merely serviceable.

Adapted from two novellas by the Jewish author Irène Némirovsky (who would later die in Auschwitz), it's set in 1940, in the fictional town of Bussy. Lucille Angellier (Michelle Williams) is a painfully timid young woman whose husband has disappeared in the war. In his absence, she lives under the thumb of her domineering mother-in-law, and one of the richest landowners in the area, Madame Angellier (Kristen Scott Thomas).

For a while the townspeople have assumed the war is happening somewhere else. That all changes as refugees start flocking in from Paris, brutally followed by German warplanes, then by a Nazi regiment that takes control of Bussy. Not only has the war come to town, but a lieutenant, Bruno Von Falk (Mathias Schoenaerts), is billeted in the Angellier home, unexpectedly stirring the emotions of its younger occupant.

A composer before the war and a decent chap desperate for civilised company, Bruno plays his melancholy compositions on the piano at night and courts his hostess by day. Williams and Schoenaerts convey the nuances of loneliness and illicit love reasonably well, though both seem weighed down by their characters' reserve; Williams certainly overdoes the quivering reticence.

What engages one more is the tumult around them. Bruno's job is to read the letters the townsfolk have been writing to the Nazis, and to gauge the import of their backstabbing accusations, for the good people of Bussy are jockeying for position, and the more social position they have, the dirtier they are prepared to fight.

The disgrace of Vichy collaboration has been well-documented; this is a different facet of wartime self-interest. It has already manifested itself in material ways - Madame Angellier evicting a family so that she can install a refugee on double the rent, the town's mayor (Lambert Wilson) foisting his billeted officer onto his least favourite tenants, the gentry hoarding supplies while the farmers starve.

The most sympathetic characters are farmer Benoit Labarie (Sam Riley) and his wife Madeleine (Ruth Wilson), both angry and rebellious. Wilson has the flesh-and-blood personality that Williams lacks, and more fire than the rest of the cast put together.

That consummate pro Scott Thomas also has her moments, albeit verging on caricature - cutting a black-clad, Wicked Witch of the West figure as she roams the countryside terrorising her tenants. At one point she even prompts Bruno to lament, "I'm the one everyone's supposed to be scared of."

It's an atypically comic moment in a film that could use some leavening. Overall this is an increasingly sleepy affair, punctuated by too few scenes of genuine tension. Director and co-writer Saul Dibb doesn't make quite the fist of his subject as he did his contemporary urban drama Bullet Boy, or his 18th-century costume piece The Duchess, failing to find a visual language to creatively convey the desired atmosphere of conspiracy, betrayal and fear.