Tasked with enforcing criminal law, public prosecutors worldwide enjoy broad discretion. Existing literature on prosecutorial discretion and accountability tends to discuss the regulation of prosecutorial discretion or analyse the influence of the procedural environment in which public prosecutors operate. This paper focuses on occupational culture as an important factor affecting prosecutorial decisions. It draws particular attention to an understudied aspect of prosecutors’ professional identity: legitimacy and, specifically, self-legitimacy, ie the belief public prosecutors have in their own legitimacy to make decisions in individual cases. The paper presents research findings from direct observations and interviews which reveal a sense of a loss of self-legitimacy amongst Crown Prosecution Service (CPS) staff due to the constant monitoring of their decisions by colleagues and managers. This all-pervasive managerialism, paradoxically, undermines the very legitimacy (and, relatedly, transparency) which the CPS has had to work so hard to develop since its inception.