"Benefit Thieves"

Something unexpected, the bus bench ad outside International House London and several others in the city are devoted to catching "benefit thieves"--"Can you tell which van is our surveillance van?" "Can you see our surveillance agent?" I assume benefit thieves are persons signed up for relief or unemployment whilst actually working (Do you like the "whilst"? I am learning already!). But at SSA and in American social policy circles we sometimes think that we are the only country to engage in this kind of surveillance or policing of benefit recipients, and the cheerful Orwellian nature of these ads was rather shockling to me.