No / The prevailing economic and budgetary climate is intensifying the search for methods and practices aimed at generating efficiencies in public sector provision. This paper investigates the increasingly popular bundle of techniques operating under the generic descriptor of lean, which promises to improve operational quality processes while simultaneously reducing cost. It offers a critical appraisal of lean as a fashionable component of public sector reform and challenges the received wisdom that it unambiguously delivers ‘efficiencies’. Quantitative and qualitative research in HM Revenue and Customs (HMRC) centred on employees' experiences has indicated the extent to which work has been reorganized along lean principles. However, employees perceive that changes in organizational processes and working practices have unintentionally generated inefficiencies which have impacted on the quality of public service. These suggested outcomes raise wider concerns as lean working is adopted in other public sector organizations.