Writers are notoriously impossible to make good movies about, and director Philip Kaufman in his disastrous new film has tackled a challenging pair: Ernest Hemingway (Clive Owen), the Nobel Laureate and world-class self-mythologiser, and Martha Gellhorn (Nicole Kidman), the American war correspondent who became, briefly, the third of his four wives.

Kidman’s Gellhorn is a long-legged blonde with a backpack, scarlet lipstick, and a focus-pulling arse in well-cut trousers. Hemingway, for all his noisy macho schtick, has a Catholic wife and kids at home. When the deep-sea fisherman and the “big creamy bitch” lock eyes in a Key West bar, even Papa’s acolytes can’t hold him back.

But Gellhorn has heard what Franco’s fascists are up to, and she’s on her way to the Spanish Civil War. The next time Hemingway sees her, she’s scrambling out of a tank in Madrid, right outside the hotel where he’s holding court with a bunch of lefty documentary-makers.

Bombardment. Interminable sex under cataracts of smashed plaster. Soon the two are a heavy-drinking, tough-talking team, radiating glamour and bravado. Their companions include the American writer John Dos Passos, the Hungarian war photographer Robert Capa, and sinister Russians including Robert Duvall as a be-medalled general who, in a shameless fit of scenery-chewing, hits on Gellhorn and is challenged to Russian roulette by the raging Hemingway.

Gellhorn is shaken up by the shelling and can’t write. “There’s nothing to writing!” bellows Hemingway. “All you do is sit down at your typewriter and bleed!” The quiet photographer Capa (why isn’t she with him?) offers more thoughtful advice: “If your pictures aren’t good enough, you’re not close enough.”

Franco wins. Still, the world is full of wars and revolutions. Kaufman slides Kidman and Owen digitally into grainy black-and-white newsreels from the 1930s and ’40s – Finland, China, the Normandy landings, the opening of the concentration camps. But reality trumps art. Beside the shocking beauty, the rawness and the horror of the documentary material, the scripted parts of the movie look not only ludicrous but indecent.

Owen might have been a convincing Hemingway, even in a green camo-netting bandana, if his dialogue hadn’t been cobbled together from Papa’s famous aphorisms, which he grinds out through clenched teeth.

Gellhorn was probably as big a pain as Hemingway, but did she really deserve Nicole Kidman? It’s excruciating to watch Kidman bulge her eyes and drop her jaw and puff out air between her collagen-swollen lips. And when that pert little face is superimposed over news footage of emaciated, naked corpses being toppled into a mass grave, we seem to have reached the outer limits of vulgarity.