Visitors could be forgiven for believing they had stumbled upon an antiwar rally. “State Britain” (through August 27), by the British artist Mark Wallinger, is a meticulous replica of the one-man peace camp created by Brian Haw that stood outside Britain’s Houses of Parliament from 2001 until last May, when police removed most of it on the ground that it violated a 2005 act banning unauthorized protests within a kilometer of Parliament Square. (Haw’s still keeping his vigil, but he’s confined to a three-meter-by-three-meter space.) “If a gallery’s about making something visible that’s been rendered invisible, this belongs in a gallery,” says Wallinger.

“State Britain” is, on one level, a paean to the loneliness of long-term obsession. The work’s handmade quality–the teddy bears, the armless doll, the handwritten notes supporting Haw–evokes a shrine, commemorating not just the dead of Iraq, but protest itself. Stashed behind the placards is a sleeping bag, weather-beaten umbrellas and yellowing newspapers. Supermarket bags filled with his rations of oats, noodle soups and peanuts dangle from the barricades. A large plastic jug filled with an unidentified yellow liquid–urine? brackish washing water?–is emblazoned with the words NOT FOR DRINKING. From the supplies, “it looks as though Haw’s been in conflict,” says Wallinger. “Camped out there, he’s a bit like a soldier.”

But what makes “State Britain” art as opposed to public protest? At the Tate, there was never any debate: it was art because Wallinger, among Britain’s most respected conceptual artists, had proposed it. Since his star rose in the 1990s, Wallinger, 47, has been considered the most political of the Young British Artists. While his YBA contemporaries busied themselves sticking cows in formaldehyde and documenting their sex lives, Wallinger explored themes like Britishness and privilege. In “Capital,” he had friends pose as homeless people and then painted them in the style of boardroom portraits. “State Britain” ’s curator, Clarrie Wallis, sees Wallinger as a descendant of 19th-century artists like Théodore Géricault and Edouard Manet, who used massive canvases to pose provocative questions about contemporary events.

If “State Britain” is a replica of Haw’s site, it’s fair to ask who really created it: Haw or Wallinger? Curator Wallis argues that Wallinger’s aim is to create “a three-dimensional history painting that represents the event, and not necessarily to continue the protest per se.” Art historian Julian Stallabrass sees “State Britain” as part of the tradition of appropriation dating back to Marcel Duchamp, who coined the notion of “readymades”–objects that become art because they’ve been selected by artists. Wallinger and his team scoured eBay for just the same brand of plush toy badger and weathered banners by soaking them in puddles.

Seeing the work in a museum gives it new depth. Afforded the Tate’s space, hush and time–none of which is available in Parliament Square–viewers of “State Britain” are forced to confront Haw’s nightmare vision of the world. For Haw, who gave Wallinger his full support, the political message is clearly more important than the messenger. “Go see it at the Tate!” Haw proclaimed after a recent court hearing, when a judge upheld his right to continue the protest. The ruling aims to preserve his civil rights, but it’s the Tate that’s preserving the full-blown expression of his anger.