LONDON (AP) -- Christiaan Nagel scrambles up an aluminum ladder, carrying a big blue mushroom.
In seconds, the 29-year-old sculptor is on the roof of a once-handsome, now neglected Victorian building in London. Under a crescent moon, he works quickly; within minutes the polyurethane fungus stands tall over the street below -- an impromptu landmark to be enjoyed and photographed by passers-by.
Nagel is a street artist, one of a growing band of painters, stencilers and sculptors bringing vibrancy to the recession-tattered streets of Britain.
His work pops up unannounced, and in that it captures the spirit of the times.
Unauthorized art in public places is booming in austerity Britain. As public funding dries up, businesses struggle and economic uncertainty hits collectors' pocketbooks, London's streets have been colonized by artists. Empty stores become pop-up art shops, empty walls pop-up galleries -- and every street artist dreams of becoming the next Banksy, the anonymous graffiti-sprayer whose work sells for six-figure sums.
Nagel, like other street artists, insists he is not motivated by money but by a combination of ego, excitement, and the desire to have his work seen by as many people as possible.
His mushrooms cost just a few pounds (dollars) to make, but generally earn him nothing. He pays the rent by trading second-hand guitars, and by occasional paid art commissions.
He makes mushrooms because they are both a pleasing shape and a flexible metaphor.
"They're pop-up art, they could be mushroom clouds, they could be psychedelic drugs," he said. "I suppose they tie in with the subculture of street art, which is guerrilla art, which is illegal."
Illegal, maybe, but increasingly accepted. Nagel says he has been stopped by police only once, handcuffed by officers while installing a mushroom in the middle of a busy traffic circle.
"They were like, 'What are you doing?' and I said: 'I'm an artist and I've just installed my mushroom.'" said Nagel, an outgoing South African with russet hair and a taste for brightly colored shirts. "They gave me a look for about 10 minutes and they let me go."
The global financial crisis, and the British government's budget-slashing, have hit the arts hard. More than 200 British arts organizations have lost government funding, and dozens say they may have to shut down.
But a do-it-yourself, street-level arts culture is flourishing. Some of London's hipper, scruffier quarters have become so art-encrusted that they are now tourist attractions in themselves, with a burgeoning street-art economy.
Around the east London districts of Shoreditch and Hackney, where canal-side lofts, media businesses and trendy bars mix with derelict factories and run-down housing projects, walls sprout giant birds and furry rodents, brightly colored hands and fantastical landscapes.
One recent morning about 20 well-dressed young tourists were on a walking tour of brick walls and vacant buildings adorned with colorful drawings and murals by artists with names like Stik, Sweet Toof and Phlegm.
The works are the product of young artists attracted to London by its vibrant art scene, and to the streets by a blend of a freedom-loving philosophy and the opportunity provided by so many neglected walls.
"The streets are the biggest gallery, the least pretentious," said Richard Howard-Griffin, who organizes the walking tours and has developed a website guide and an iPhone app to London's booming urban art scene. "They are able to reach people who don't go to galleries."
The downside of street art is its impermanence. What's here today may be gone tomorrow. Nagel says he has installed more than 100 mushrooms, but only a handful are still standing. The longest-surviving has overlooked a busy road for more than a year.
But that's also part of its appeal. Spotting a new Banksy before it is covered up or spirited away -- building owners have been known to remove whole walls to preserve a stencil -- is a bit of a sport. Street art also brings its practitioners a wide audience, the thrill of covert action and a sense of community.
"There's a great energy here," Nagel said. "There are some great street artists from all around the world who come together here."
Many street artists are reluctant to speak publicly. They are, by nature, anti-authoritarian, and their work thrives on secrecy and the mystique of a pseudonym.
Nagel says he finds such silence difficult. "I get too excited about my work. I want to tell everybody."
His mushrooms are the product of serendipity. He grew up surfing the Indian Ocean off Durban, and began experimenting with the kind of foam used in surf boards. One mold produced a mushroom-top shape, and he was smitten.
Now he makes the sculptures on a resin-stained rooftop outside his apartment and leaves them dotting rooftops, bridges and even trees.
Before last year's wedding of Prince William and Kate Middleton, he left the royal couple a gift in the middle of the Serpentine, the artificial lake in Hyde Park.
"I put on my wet suit, got on my surfboard and paddled out," he said. Nagel lined up 10 in a row along an island, with a sign declaring them "a present for the couple to be married." It was all gone by noon the next day.
Despite the occasional insult or hurled bit of litter, Nagel says the reaction of the public is overwhelmingly friendly.
That sentiment is seconded by Run, a thoughtful Italian-born artist who has been painting bright murals of hands and faces across London for several years.
Run -- he prefers to be identified by his artistic pseudonym -- decided early on that he didn't like painting at night. It was too solitary, too spooky. He paints in daylight, and says most onlookers have a positive reaction.
"You discover that people really want to smile," he said. "If anything makes you smile, and it's a bit different from normality, people are happy and you can see it."
Local authorities and building owners are increasingly likely to protect a colorful mural, rather than paint over it. Since Banksy, high-quality street art has been seen less as vandalism, more as a feature that can add cachet and value to a property and cachet to a neighborhood.
Officially commissioned street art has been used by Olympicsd organizers to get young people excited about this summer's 2012 London games. Unofficial art increasingly escapes the paint-rollers of local-authority cleaners. A spokeswoman for the mayor's office, speaking on condition of anonymity because of mayoral election restrictions, said street art was "part of the fabric of London."
Today's street art grew out of the New York graffiti scene of the 1970s and 80s. It is now global, and the Internet has helped street artists gain an international profile. Artists like the Belgian Roa and the Brazilian twins Os Gemeos travel the world making their mark.
Museums and galleries have begun holding exhibitions of street art, and street artworks have become increasingly valuable -- which leaves some worrying that the movement has lost its soul.
Many street artists look with a combination of suspicion and respect at Banksy, who has managed to retain an outsider image even as his satirical stencils -- policemen kissing; riot police with yellow happy faces -- change hands at white-walled galleries and high-end auction houses.
The graffiti artist has made a fortune and won celebrity fans including Angelina Jolie without ever revealing his identity. (It's generally accepted that he is in his late 30s and from the English city of Bristol.)
He still stencils buildings and bridges, but also creates portable works intended for sale -- often for tens or even hundreds of thousands of dollars. He drew a title sequence for "The Simpsons" and directed the acclaimed documentary "Exit Through the Gift Shop."
"Banksy has been groundbreaking in terms of what he has done for public perceptions of street art," said Gareth Williams of auctioneer Bonham's, which recently sold 17 Banksy screen prints and works on canvas for a total of 400,000 pounds ($640,000). "He's a household name."
No one else has yet reached that level, though many artists hope to emulate Banksy by having one foot on the street and the other in galleries. And the mainstream is drawing ever nearer. A few years ago, London street artist Ben Eine began painting colorful blocky letters on the metal shutters of East End shops. When Prime Minister David Cameron visited Washington for the first time after being elected in 2010, he gave President Barack Obama an Eine painting as a gift.
Williams says the market is going to continue to boom. For collectors who find much contemporary art alienating, with its pickled sharks and enigmatic installations, street art has an appealing freshness and immediacy,
"It's very, very accessible," he said. "People can relate to pieces they see on the street."
Artists worry that the increasing commercialization of street art risks killing the magic.
Nagel does accept private commissions, and recently sold a mushroom for 900 pounds ($1,440) to a wealthy asset manager with an Andy Warhol on his office wall.
But he says a sense of excitement and "the magic of the unknown" keep him going out onto the streets.
Run calls his art "the opposite of an advert" -- designed to give viewers pleasure rather than get them to buy something. But he's aware he's not motivated solely by idealism.
"It's a big ego thing," he said. "My aim is to see my painting really big in the public space -- and eventually get money from that."
Run worries about street art becoming commercialized, but can see the positive side. The business of street art is providing jobs in tough times.
"A friend of mine just arrived in England," he said, "and the other day she was at the Job Center. And she found a vacancy asking somebody to do street art tours around east London. ... Plumber, van driver, bar attendant, catalog distributor -- now street art tour manager. It's great."
Jill Lawless can be reached at: http://twitter.com/JillLawless