It has that elusive cred factor, is endorsed by the likes of Brangelina, and fetches dizzying prices – there’s no mistaking the frenzy surrounding graffiti art. Still, a few eyebrows were no doubt raised at Bonhams auctioneers when it decided to host a sale of the phenomenon known as urban art. After all, this kind of work in its purest form (on the street rather than on canvas) is illegal.

However, Gareth Williams, a senior specialist in urban art at Bonhams, says its outsider status – with many of its practitioners, such as Banksy, anonymous – only adds kudos, and value. “Everyone loves a rebel, and their mystique only adds to the attraction.”

The sale includes work by the graffiti-art pioneer Keith Haring, as well as recent artists such as Paul Insect and Faile. “Their work is more accessible than some conceptual art,” says Williams. “And these artists share a political edge and a wry sense of humour, which appeals to a new generation of collectors.”

Darius Grant, the collector and Wall Street hedge-funder who owns work by the 1980s New York legend Jean-Michel Basquiat, has noticed a growing interest in urban art among his peers. “If you work in this world, you probably like taking risks, but you’re still part of the Establishment – it’s quite conservative. You can’t rebel at work, but you can buy rebellious art that’s shocking or subversive.”

This is good news for the artists – and not just in terms of sales. Those with suitable street cred are increasingly in demand in commercial spheres. Take Inkie, who made his name on the innovative Bristol scene, along with Banksy, 3D and Nick Walker. Besides his private commissions, Inkie is now head of graphics at the computer-games company Sega. He also has his own T-shirt label, Flying Eyeball. At 37, Inkie, like many on the scene, has had run-ins with the law over the years, but these days, he is based in London and no longer does anything “naughty”, as he puts it: “I’m too old, and I’ve got a job and a kid now.”

Is there a danger that commercial interest will force compromises? “It’s become a lot bigger than I imagined it would,” Inkie admits. “It does make me laugh when design agencies say they want ‘Banksy-style’ graphics.”

The urban-art ethos has always been about “reclaiming” public space, or “taking what’s ours”, as Inkie puts it – and you could argue that that’s exactly what these artists are doing now.

The Urban Art sale at Bonhams is on Tuesday; www.bonhams.co.uk

NAMING NAMES

BANKSYThe king of the urban art scene and master of the guerrilla stunt. Find his work on the streets of London, Bristol and other cities around the world, most recently, Bethlehem. A Banksy-daubed wall has sold for £208,000 on eBay, with the proviso that the purchaser remove it.

PAUL INSECT A recent solo show had to be cancelled after Damien Hirst bought the lot.

FAILE New York collective – highly collectible.

ADAM NEATE Subverted the genre by painting on cardboard and canvas and hanging these in public spaces.

TAKASHI MURAKAMI Japanese artist who fuses pop and manga imagery.

3D Aka Robert del Naja of Massive Attack, represented by the same management as Banksy (www.lazinc.com).

NICK WALKER Spray painting and stencils. His Moona Lisa is in the Bonhams sale.

INKIE Early innovator and creator of wild style art nouveau, much in demand (www.inkie.co.uk, www.flying-eyeball.com).

BLEK LE RAT INFLUENTIA LThe veteran French artist has inspired Banksy, among others. His works are in the Bonhams sale.

DAN BALDWIN Prints, paintings and ceramics(www.danbaldwin.net).

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