More than a decade after the death of a princess inspired thousands of grieving strangers to leave tributes of flowers, cards and messages outside Buckingham and Kensington Palaces, the flowery shrine has become a commonplace sight on dangerous streets. Sprays of carnations, roses, lilies and orchids seem to spring out of the prosaic municipal fixtures and fittings, like living creatures insisting on their power to transcend death.

Andy Barter is a successful commercial photographer whose work has appeared in award-winning ad campaigns (such as Heineken) and the pages of Wallpaper*, Arena and Esquire. His art work tends to push simple subjects – paint splashing from a bottle, the silhouette of a naked body – into abstract and surreal forms. Show him a floral roadside tribute, however, and he'll photograph it with loving realism, as if it's a French or Dutch still-life.

"Why floral tributes? Because I find them very moving and sad," he says. "You can be sitting in your car, totally cosseted from the world, getting frustrated with your journey, and one of these appears, to remind you that awful things happen on the road, much worse than being stuck in a traffic jam. I decided to photograph them in the most sensitive way I could, because they've been put there by people experiencing probably the worst time of their lives."

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Barter doesn't reveal much about the circumstances of the deaths so eloquently memorialised in his work. He lets the tributes express their own ramshackle melancholy: the notes in children's handwriting, the details of a truncated life inside a polythene case, the spooky digital photo. The sheer variety of tributes surprised him. "Some were no more than a simple bunch of flowers, gaffer-taped to a lamppost. But one, in south London, was a really elaborate shrine: a bench, little statues, religious mementoes, poems, photos, around this tree that the car must have run into ..."

Though the dark backgrounds suggest the middle of the night, he took the pictures in late afternoon. "We used a flash, with my assistant holding a light on a boom above the flowers, to make them feel more God-lit, if that makes sense. It isolated them from their environment."

Barter cleverly contrasts the drama of the flowers and the everyday tedium of the park railings, tarpaulins, bollards and no-right-turn signs that are the language of the road. The flowers are gloriously lit, in triumphant pinks, yellows and greens. Some of the displays seem a touch too perfect, in combining dead flowers with live ones. Had he ... you know ... adjusted the displays? "No, no," says Barter, indignantly. "I didn't want to touch them. When you photograph them you feel a sense of responsibility: the last thing you want is to be seen as some kind of ghoul." He noted, however, that bereaved relatives would sometimes respond to the decay of their tribute roses by introducing new live ones. The combination, he agrees, is too symbolic: it's fitting that the French for "still life" is nature morte.

I wonder if Barter had taken pictures of the Diana flowers in 1997. "No," he says. "It's not something I'd done before. Even now, I find these tributes puzzling. If someone I'd known had died, I'm not sure I'd want to mark the spot in that way – though, to me, the mystery only makes the shrines all the more haunting and intriguing."