This contribution explores how technocratic economic governance rests on underlying principles of political economy—normatively informed judgements about how the economy and policy operate. It shines light on how fiscal councils such as the OBR can open up (or close down) policy possibilities through the way they narrate economic crises, the trajectory of the economy and the fiscal stance. Noting the epistemic limits of technocracy, it shows how fiscal forecasting is based on a presumed knowability and legibility of the economy and the fiscal stance looking years or decades ahead—a questionable and problematic presumption. It highlights increasing tensions between expert oversight and populist and ‘post truth’ politics within Britain’s economic governance regime since Brexit. The Office provides oversight, and a form of accountability for government policy, and is itself accountable to parliament. Nevertheless, many of its key and consequential assumptions are obscured from democratic debate and oversight. The Office, and UK economic governance, would benefit from more robust mechanisms of democratic engagement and deliberation. Under-developed democratic accountability is a source of crucial fragility for technocratic economic governance. The piece ends by exploring the scope of OBR fiscal assessment of climate change and its costs—underlining the ‘politics of economic method’ and how subterranean methodological techniques in putting OBR economic ideas into practice can be of first-order political and policy significance. They can shape policy possibilities for tackling climate change for decades to come.