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Jane Campion has turned the short and doomed affair between John Keats and Fanny Brawne into an enthralling film that tenderly rips your heart to shreds. A period piece about a sickly Romantic poet and his obsession with the girl next door is not exactly a scenario that sets pulses racing on the Croisette. The surprise is just how exhilarating and tragic this true story actually is.

Keats and Brawne fell in love when they lived in separate parts of the same house in Hampstead village in 1819. Two years later he died of tuberculosis. Although Campion neatly hinges Bright Star on Keats’s love letters and verse, her stroke of genius is to film the romance mostly through Fanny’s eyes. By so doing Campion captures the shy and extraordinary intensity of the relationship itself.

The two leads might well steal the top acting prizes in Cannes. The chemistry between them as they edge from simple, formal visits into a secret affair is pitch-perfect. Abbie Cornish is magnetic as the headstrong 18-year-old muse who shyly teases Keats about the quality of his verse. There is a dash of Nicole Kidman about her performance, and the way she can never quite hide the emotions raging behind her eyes.

Ben Whishaw is magical casting as the penniless and crumpled 23-year-old poet who is forced to rely on the charity of others, mostly his best friend, Brown (Paul Schneider), who jealously monopolises Keats in return for putting him up. It is this duel between Brawne and Brown for Keats’s heart that gives the film its most flinty and revealing moments.

Schneider’s sniping Brown plays all sorts of cruel tricks and mind games to keep the would-be lovers out of each other’s reach. He throws insults at Fanny when she asks Keats for lessons in poetry. Cornish’s persistent Fanny gives as good as she gets, shredding Brown’s pathetic efforts at writing poetry. It’s great spice.

By contrast, the romance between Keats and Fanny is pure Romeo and Juliet. Whishaw’s charismatic poet simmers with mystery and desire on rambling walks over Hampstead Heath.

There are chaste, lingering kisses in the woods. A coy holding of hands. Keats’s poetry hits a purple high where we watch as he composes Ode to a Nightingale under a tree in the garden, and the title poem Bright Star stretched out on a sofa with his head lolling in Fanny’s lap. In stark contrast, Brown’s grubby affair with one of his kitchen staff looks morally bankrupt and seedy.

The kind of spiritual intimacy between Keats and Brawne is a refreshing spectacle in a festival where it seems almost de rigueur to frame every serious romance with graphic sex. The most poignant detail of all is that their relationship remained unconsummated. After contracting tuberculosis the act would literally have killed him, as would another winter in England, so Keats is obliged to go to Rome. Fanny never sees him again. The scene in which Cornish hears the news of his death melted the auditorium.

Campion films the melodrama with admirable restraint. Visually, her film is as spare and sensual as the poetry that she manages to stitch into the film with a thrilling lack of fuss. After a recent run of indifferent form, the director is back to her best.

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