If art-prankster Banksy’s first film is a hoax, as it just might be, it’s an extremely complex and clever one. With echoes of the Frankenstein story.

Exit Through the Gift shop apparently began life as a documentary project about street art by fan and film-maker Thierry Guetta. By the end, Banksy is chronicling Guetta’s self-reinvention as an artist whose glib pop culture artworks – all knocked off at speed by hired helpers – sell for thousands. “Maybe it means art is a bit of a joke,” the disguised and bemused Banksy opines on screen. Well, quite.

French-born Guetta, a married father of three who runs a vintage clothing shop in Los Angeles, has a compulsive need to film everything. In the 1990s he began to video the underground street artists who painted graffiti murals and large scale stencils on public walls. Quickly graduating from observer to helper, he volunteered as assistant to the elusive Bansky when the anonymous artist made his first visit to America in 2006, adding footage of him to his countless hours of tape.

Gallery: Exit Through The Gift Shop premiere

Guetta’s first attempt to edit his amorphous mass of imagery into a coherent whole convinced Banksy his friend was not a film-maker “but someone with mental problems who happened to have a camera”. He encouraged Guetta to make his own art, and created a monster. The Frenchman’s first exhibition, under the name Mr Brainwash, though chaotic and absurdly ambitious, made him an overnight success.

The pleasure of the film is threefold. The scratchy footage of street artists defying injury and the police to adorn or deface public spaces is a thrilling record of a spontaneous, secretive revolution in contemporary cultural life. Then there’s the mangled and hilarious Franglais commentary of the mutton-chopped Guetta, who resembles a Gallic version of porn star Ron Jeremy. And underlying it all is the awareness that the irony-free art market can take something anarchic, illegal and free, and put an auction-house price on it.

Unlike Guetta, Banksy proves a skilled editor and organiser of material. Having repeatedly skewered the art world in his own super-smart creations, it looks like the film world could be next.

Exit Through the Gift Shop is on general release from March 5.