Santiago Sierra: Dedicated to the Workers and the Unemployed

Across three rooms of the Lisson Gallery, a retrospective of 53 films by the Spanish artist reveals a panoply of traumatic 'artsploitation' scenarios including minimum-wagers, homeless people and junkies being renumerated for holding up walls, being tattooed, living in a ditch, having their heads shaved or being smuggled in the hold of ship - collectively titled 'Dedicated to the Workers and Unemployed'. Anyone unfamiliar with Sierra's unforgiving frontality should spend an hour in front of some of these shaming, humbling films - necessarily lonely, if never less than frightening, experiences.

In many ways, Sierra's crude, monochromatic aesthetic of friction has become a model for much of the heavily-politicised work coming out of Mexico, but he will never be content to dwell in a geographical ghetto for hot-tempered Latin artists. Since 2009 Sierra has been towing a half-tonne public sculpture to some 40 towns and cities around the world, simply spelling out the word 'NO' in giant, black letters (now sat forlornly in the gallery covered in scratches and graffiti). The message is clear: 'no' is not just a negative force, but also a call to arms. No más, no compromise, no sell-out, no retreat, no surrender.