Directed by Maïwenn. Starring Karin Viard, Joeystarr, Marina Fois, Nicolas Duvauchelle. 16 cert, limited release, 127 min

YOU HAVE TO admire the ambition on display in the third feature by the French director, formerly a model, who calls herself Maïwenn. Involving a large array of characters, the picture sets out to depict life in the juvenile protection unit of the Parisian police.

Maïwenn’s sprawling piece believes itself to have everything. There are moments of black comedy. The officers encounter various domestic dramas. Inevitably, Polisse takes in a degree of social commentary. Unfortunately, it all gets a bit much: the film suffers from a lack of focus and a tendency towards melodrama. Few viewers will endure the final, absurdly sudden catastrophe without gawping or sniggering down the back.

The director plunges us straight into the drama with a sequence in which a child haltingly discusses apparent abuse at the hands of her father. We are then gradually – not to say randomly – introduced to various hardworking officers. Nadine (Karin Viard) is enduring a troublesome divorce. Chrys (Karole Rocher) has just discovered that she is pregnant. Fred (rapper Joeystarr), recently separated from his daughter, can’t separate his emotions from his professional life and frequently ends up in clashes with his by-the-book boss (Frederic Pierrot). Maïwenn plays a photographer covering the unit who – as if there wasn’t enough going on – ends up having an affair with one of the cops.

There are moments of real intelligence in the picture. Maïwenn allows the officers, stressed to breaking, to laugh uproariously at some of the evidence they survey. Using a mobile camera and energetic editing, she invites the actors to play off one another in admirably naturalistic style.

But Polisse, which unexpectedly won the Jury Prize at the 2011 Cannes Film Festival, feels desperately in need of some quality control. Some of it plays like a Gallic version of The Wire. Too much of it comes across like an unlikely mash-up of EastEnders and Starsky Hutch. M’eh, though not quite merde.