The pavements near where I live in north London are unremarkable but for one thing. The disgusting splodges of chewing gum ingrained on drab, dusty paving stones serve as a canvas to the street artist Ben Wilson, who regularly creates miniature murals on them.
Wilson can often be seen dressed in Guantánamo-orange overalls, stretched out on the roadside with a paintbrush in hand. He and his colourful offerings, which feature local landmarks, political statements and cartoonish caricatures, are well-known in the area. Children call him "the chewing gum man".
As with most street artists, Wilson's work is uncommissioned, unsolicited and illegal. One of the joys of it, and that of other urban artwork, is the surprise of encountering it under otherwise ordinary circumstances. In Bristol and London, where the UK "scene" is at its most vociferous, you won't just find Banksys but a huge range of daubings, murals, stencils, stickers and installations by any number of creatives known by pseudonyms to safeguard them against arrest. Their work is provocative, political, uncensored and usually exacted under cover of darkness. Viewed as vandalism by many, street art is steeped in punk, anarchy and iconoclasm. Because it ideologically sticks two fingers up at the Man, it seems anathema that street art should become increasingly commercial.
This month, a touring exhibition of the Victoria & Albert Museum's collection of street art prints, which includes pieces by Banksy, D*Face, Ben Eine and Shepard Fairey, makes its UK debut at the Herbert Art Gallery & Museum in Coventry. To accompany it, the gallery has specially commissioned six new works by emerging street artists.
I found this news surprising. After all, a gallery commissioning street art undermines the nature of the genre, doesn't it? Exhibiting art influenced by graffiti and tagging is one thing, but offering up white walls to be spray painted is another. When Faile was asked to exhibit at the Tate Modern in 2008, the gallery was sensitive enough to offer up its external walls rather than its interior ones.
"Street art belongs on the street," says Ben Eine, an artist who hit the headlines when David Cameron gave one of his paintings to Barack Obama during a visit to the US in July. "But I'm a working street artist and I earn my money selling art in the style of street art via galleries. I don't get paid for what I do in public places. So I invest the money I earn in galleries back into doing the stuff I passionately want to do on the street."
Eine thinks his approach negates accusations of selling out. He says: "If that's how artists are going to work, then I think it's cool. But if they're just a bunch of so-called street artists that make stuff in their studios and sell it in galleries, then they're making a bad choice."
Gill Saunders, senior curator of prints for the V&A, told me she had no idea the Herbert had commissioned new work to go alongside the collection the museum had put together. She wasn't alarmed at the news, but was interested in what she called the "life cycle" of such works, and whether they would be destroyed or sold after the show.
"I suppose there are two angles on this," Saunders said. "On the one hand, I'm wary of commissioning such work as I think it should exist out on the streets for its own sake. On the other hand, you could say that street art is partly ephemeral, but it's also a kind of performance art. In that sense, I think it's perfectly valid for a gallery to commission something to mark an event in that way."
The Herbert is not sure what will happen to the artwork post-show. Much of it is being made on MDF boards rather than real walls, so can be peeled off and taken home by the artists afterwards. If someone wants to buy one of the pieces then they can do so privately via the artist, but as it is a public gallery the Herbert would have no hand in this.
Pahnl, one of the artists commissioned by the Herbert, says he hasn't had any criticism from his friends in the scene. "Graffiti writers and taggers see anybody who enters the gallery environment as selling out. But street artists embrace the idea more, often because they have a fine art background."
Flogging prints on the side to finance free work is the understandable toss-up faced by many such artists. Yet because it is an underground art form, it's possible that embracing commerciality in this way will go some way to normalising and censoring the statements such artists can make.
Wilson is not idealistic about the making and selling of street art, but he says that what he has striven to do over six years would not have been possible if he had expected payment. The issue over whether street art should be commissioned is thrown into a new light when Wilson explains that he takes commissions all the time – from people in the street.
"People come up to me in the street because they want a picture; this can be because their friend's just died or they've had a baby or they want a love message for someone," he says. "The majority are school kids, the homeless or local taggers, so I'd never take any money from them. But if somebody does want to give me money then that's fine."
Wilson says it can be difficult to fulfil his commitments to such commissions when he's short of money, because he has to pay for paint and because has a family to support. He says he's been questioned by police around 900 times, but laughingly tells me that even the police have started commissioning him.
The integrity with which he views his work is impressive, as is his criticism of corporations, advertising and the government. This is the crux of his need to produce street art: he feels a need to produce art simply to exercise his creative muscles. He'd never put a price on his gum paintings "because I wouldn't want them to be like everything else", but he wouldn't rule out exhibiting in a gallery.
If street art is born from a subculture defined by covert tactics and illegality then it is going to be painful putting it into a conventional setting. Die-hard fans will be appalled but it seems that in the world we live in, at least part of the movement needs to reach out to commerciality if only so that the artists can feed themselves and buy paint.
Eine, who paints stylised topography spelling out politicised statements, struggled to find a painting innocuous enough for the Camerons to give to the Obamas. He settled on one emblazoned with "Twenty First Century City." With the Prime Minister endorsing a street artist who has been arrested on more than 15 occasions, the times must certainly be changing.
Street Art: Contemporary Prints from the V&A and new work by Fresh Paint, Herbert Art Gallery & Museum, Coventry (024 7683 2386; www.theherbert.org) 9 October to 16 January