The starting point for legal analysis of UK administrative rule-making remains the presumption that discretion must be retained, as expressed in the no-fettering rule. Nevertheless, judicial attitudes have changed substantially since the landmark case of British Oxygen Co Ltd v Minister of Technology. Whereas the no-fettering rule historically deprived administrative rule-making of any significant legal status or effect, the permissive approach ushered in by British Oxygen Co paved the way for increasing judicial regulation of administrative rules, culminating in the contemporary position in which adopting rules or policies may sometimes be mandatory. Despite these changes, the law in this area remains unsatisfactory. While the no-fettering rule continues to frame and shape judicial intervention, it exists in considerable tension with newer legal doctrines and its scope and functions appear to have altered. Moreover, judicial regulation of administrative rule-making is still patchy and incomplete, and its conceptual basis is often unclear. This article therefore proposes a fundamental reconceptualisation of judicial control of administrative rule-making, which draws a sharper distinction between whether administrative actors should seek to structure their discretion through rules and how administrative rules should be regulated if adopted. On the former question, it advocates abandoning the no-fettering rule in favour of residual, rationality-based control over the degree of structuring which is appropriate in particular contexts. However, it recommends extending and systematising judicial control over administrative rules which have been adopted, employing a functional analysis to generate regulatory standards.