Exit Through The Gift Shop, 'Lambeth Palace', London

A pop-up premiere for Banksy

Last week, the graffiti artist Banksy's first film Exit Through the Gift Shop was a given a red-carpet screening in the vast Berlinale Palast as part of the Berlin Film Festival. Yesterday morning in London, as the rain lashed down outside Waterloo Station, a man in a gas mask was painting a red carpet outside a makeshift cinema in an abandoned tunnel.

The "Lambeth Palace", as Banksy has chosen to call his improvised film theatre on Leake Street, is holding special previews of Exit Through the Gift Shop for the next nine days in advance of the film's nationwide release on 5 March. At the Monday morning screening, the publicists were handing out a leaflet which, with some accuracy, described the dungeon-like auditorium as London's "darkest and dirtiest* cinema" (the asterisk told us "Cineworld Edmonton not included").

Banksy's cinema certainly isn't your typical multiplex venue. Not even the fleapits of the 1970s showing Mary Millington double bills were quite as dank and chilly as this. The foyer boasts a few of Banksy's latest artworks. Against one brick wall, effigies of the Queen and Prince Philip are seen unveiling a big white anarchist sign. On another is a big Hollywood-style sign for production company, Paranoid Pictures. In a corner is a fake bonfire, burning a selection of 18th- and 19th-century paintings, portraits of Napoleon and Queen Victoria among them. There is an ice-cream van from which a youngish man with a goatee beard serves popcorn and soda.

The Lambeth is surely the only cinema in Britain at which spectators are presented with tins of spray paint as they make their way home. Yesterday's audience members were given 400ml cans of Ironlak, the aerosol paint of choice for budding street artists. The tunnel in which the cinema is housed is an authorised graffiti area. "No sexism, no racism, no adverts," reads the billboard at the tunnel's entrance. "You don't have to be a gangster to paint here, so please don't behave like one." The pity was that most of the preview audience was too shy to let rip with the paint.

"We've got an usherette, except she sells spray paint instead of cigarettes. I think graffiti writing might actually be more socially acceptable than smoking," Banksy commented in a statement. His remarks hint at the uncomfortable and contradictory status that the artist currently holds. On the one hand, he is the outlaw: the Robin Hood of street art who refuses to be photographed and whose work is subversive and satirical. On the other, he is so lionised by the art world establishment (and now by the movie world too) that his edge risks becoming blunted.

Banksy's film explores this tension in perceptive and very funny fashion. The film's ostensible subject is Thierry Guetta, a Frenchman based in LA who became obsessed with street art in general and Banksy in particular, spent many years filming both and then turned into a wildly egotistical street artist himself.

Is the documentary a spoof? Can we trust what Banksy tells us about Guetta (whose street artist name is Mr Brainwash)? It doesn't really matter. What makes Exit Through the Gift Shop such an arresting and enjoyable film is the way it chronicles the street art movement and Banksy's part in it. Banksy himself appears on camera looking a little like Darth Vader, filmed in heavy shadow and with his his face hidden beneath a hood. A droll interviewee, he holds forth on such subjects as the £10 notes he printed with Princess Diana's face on them, a situationist prank he carried out in Disneyland, and his feelings about the mysterious Guetta.

Watching the film in Banksy's subterranean Waterloo cinema, listening to the trains rumble by overhead, is quite an experience. Banksy has organised the screenings so – as he puts it – "normal people" can see the film "before the celebrities get stains all over the furniture". Even so, you still can't help but ask why an artist who thrives on anonymity is so busy drawing attention to himself.