This paper examines the use of ICT driven surveillant assemblages in UK welfare policy by drawing on the results of empirical research conducted for the Department for Work and Pensions (DWP). The focus is on one aspect of the growing role of surveillance in social policy: data aggregation on populations characterized by sustained worklessness. The implementation and implications of this form of surveillance are examined. The paper explores surveillance systems that were extant in 2005/06 and those that were being designed. The paper argues that there is an ongoing need for critical evaluation of the underlying logic of data mashing on marginalized populations.