How do you make a movie about someone who guards his anonymity so closely that he refuses to be filmed?

Well, the answer here is that you don’t. Instead, mystery art establishment darling and Bristolian wall-dauber Banksy has made a rather fine film which traces the history of street art while having a sly dig at the modern phenomenon of clueless collectors.

French-born Thierry Guetta – a dead-ringer for portly porn star Ron Jeremy – made his money flogging LA airheads designer clobber, a lucrative business that financed his first love – cinematography.

Rarely without a cine camera in his hand, Guetta found the newly-emerging LA street art scene – championed by Shepard Fairey - an intriguing subject. It helped that Gallic urban artist Space Invader was his cousin.

Using his contacts, Guetta wanted to film the notoriously slippery Banksy, the British stencil-meister whose witty and original wall work had won over an audience far beyond cloistered art critics.

However, Banksy, aware that ill-organised Guetta has thousands of hours of un-archived footage, suggests another film, chiefly to permanently record an art form that is by its very nature ephemeral.

His first effort was a disaster so Banksy took on directing duties, coming up with an assured piece of documentary film-making that is also very, very funny.

Check out the scene where Banksy is “installing” a blow-up figure of a Guantanamo Bay prisoner in Disneyland and Guetta gets hauled off by a gang of Uncle Walt’s goons or the shot of millions of counterfeit tenners with Princess Di's face on hidden in Banksy's studio.

There’s also a wry comment on the nature of celebrity art when Guetta – with no discernible talent but an ability to employ minions to ape contemporary styles – stages an exhibition that is a bizarre hit with an LA audience who clearly don’t know a Haring from a (Rolf) Harris.

This is splendid stuff, directed with verve and humour by Banksy who – aghast at Guetta’s artistic triumph – announces he will never make another art film. Shame.

Tim Evans