This exploration of UK fiscal rules and the establishment of an independent UK fiscal watchdog focuses on the practical enactment of rules-based fiscal policy to analyse the politics of technocratic economic governance. Analysing UK macroeconomic policy rules and their operation unearths numerous dimensions of the politics of technocratic fiscal policy-making. Firstly, policy rules are marshalled for partisan purposes. Secondly, a politics of economic ideas surrounds the invention, revision and interpretation of fiscal rules. Thirdly, technocratic economic governance entails a ‘politics of method’, selecting methodological approaches necessarily built on particular political economic assumptions. Finally, a ‘politics of numbers’ sees politicians cooking the books to present their economic record favourably against fiscal yardsticks. Successive governments have altered UK fiscal rules, informed by different political economic principles. The Office for Budget Responsibility (OBR) sees itself as a technocratic and apolitical institution, yet its operational work entails contrasting accounts of the economy and policy. The scale of discretion and judgement inherent in operating fiscal rules is under-appreciated. This article finds technocratic economic governance to be a much more social and political process than many advocates of economic rules-based policy acknowledge. It engenders new forms of distinctive fiscal politics within elite statecraft and expert technocracy.