In April 2002 Jobcentre Plus started to operate in the UK bringing together the service of the Benefits Agency and the Employment Service. Offering a fully integrated benefit claiming and work placement/job-seeking service for people of working age this new organisation aims to strengthen the link between welfare and work. Due to the magnitude of the associated organisational change, the national roll-out of the new organisation is being implemented gradually over a transitional period ending in 2006. During this transitional period some local offices are fully integrated while others functions remain split between pre-existing Benefits Agency and Employment Service offices. In this paper we examine how changes in the level of integration (measured as the percentage of offices within districts offering the integrated Jobcentre Plus service) within districts over time affected performance with respect to job entry, benefit service and customer service delivery. Our analysis suggests that Jobcentre Plus has a clear positive effect on job entry outcomes for all client groups, a negative effect on business delivery while it has neither a positive nor a negative effect on customer service outcomes.