The secret location for the screening of this film – a cavernous brick vault beneath Waterloo Station – is an appropriate match to its director, the street artist and mystery provocateur Banksy.
The sense of intrigue is unmistakable, and fortunately Exit, an odd, enfolded sort of documentary, delivers on all the build-up. It is partly an account of the rise of street art in the 1990s, in which Banksy's wall painting became an integral force, and partly a cautionary tale about the difference between creativity and hype. Banksy himself, hooded and shadowed, recounts his association with Thierry Guetta, a French-American chancer who later styled himself as "Mr Brainwash" and parlayed a minimal artistic understanding into fame and fortune. His opening show in LA, which looked to be heading for calamity, somehow draws both huge crowds and the hard cash of collectors: by the end of the week a million dollars' worth of Mr Brainwash's sub-Warholian tinkerings had been sold. The exasperating element of the story is that Banksy, as he ruefully admits, encouraged this charlatan. Too much to hope he'll ever go to the wall – that's how this whole thing started.