Whatever you think of his political stance, Brian Haw’s protest against the Iraq war outside Parliament is a feat of endurance and commitment: 2,054 days and counting. But is an art gallery the best place to recreate his visually cacophonous one-man vigil?

Sure, the attention to detail is amazing in Mark Wallinger’s new installation, State Britain at Tate Britain, but isn’t it just lazy of an artist of his stature to reproduce Haw’s protest piece by piece?

Haw’s protest was curtailed vastly last year because of the introduction of the Serious Organised Crime and Police Act 2005, which Wallinger clearly believes to be iniquitous. But Wallinger, famed for his Trafalgar Square plinth installation Ecce Homo, has carefully reconstructed the full panoply of Haw’s peace camp before that happened, with more than 600 banners (“Bliar” et al), photographs, peace flags and messages from wellwishers running along the length of the Duveen Galleries. The effect of transposing this massive accretion of art from the street to Tate Britain makes you focus on the constituent elements of Haw’s protest. Here are tiny wooden crosses with poppies, plastic dolls with bloodied eyes, cuddly toys with labels such as “Dare to dissent”. There are tiny plastic containers of milk, sweeping brushes and other detritus of a protester’s daily life.

But moving Haw’s protest from the street to the hallowed hush of the Tate denudes it of rawness and energy. The riot of colour, the anarchy of words and images, are dimmed; the weatherbeaten plastic coverings aren’t flapping in the wind any more, but listlessly reflecting gallery spotlights. Crucially, Haw isn’t here. That he is in Parliament Square every day is the point of his protest. For all its crackling invective and inflammatory imagery, Wallinger’s work lacks life.

The feeling that you are witnessing a bit of a charade is exacerbated by a black line that runs diagonally across the gallery floor, marking one kilometre from Parliament. Within that kilometre, unauthorised protest is illegal. Wallinger’s intention here is not only to draw attention to what he perceives to be the erosion of civil liberties, but also to interrogate whether State Britain should count as art or protest or, as it clearly does, both.

It would be something if the police took Wallinger and Tate Britain at their literal, liberal word and removed the half of the installation that is on the “wrong” side of the line.

Whatever, the wheeze is a feeble bit of posturing. There is such consensus now that “the war” is a bad thing that an hour spent dwelling over the pictures of hideously disfigured children and anti-Blair and Bush rhetoric may leave most gallery-goers emotionally charged but hardly challenged, which surely is the artist’s real job.

Wallinger’s achievement, then, is physical: State Britain is big, richly detailed and faithful to its inspiration. But is it original? No, it’s a copy. Does it ask new questions or challenge our preconceptions? No, it merely confirms the liberal consensus. A pro-war, pro-Blair work of art . . . now that would be radical.

Tate Britain: 020-7887 8888, until August 27

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