This article engages with the Imprisonment for Public Protection (IPP) sentence of the UK Criminal Justice Act 2003, a prominent measure against ‘dangerous offenders’, in a ‘substantively political light’ (O’Malley, 1999). It provides an interpretation based on policymakers’ beliefs and traditions. I argue that the perceived need for the IPP sentence and its ultimate form was the result of New Labour ministers’ reliance on the Third Way political ideology and its implications for criminal justice policy. In addition, in terms of the policymaking process, I suggest that the ‘Westminster tradition’ conditioned policymakers’ actions in relation to the IPP sentence, in ways that were crucial to its outcome. The article concludes with an examination of the moral significance of these beliefs and traditions by reference to Bauman’s discussion of the dangers of a modern ‘garden culture’.