The Office for Budget Responsibility and the Politics of Technocratic Economic Governance is about the politics of economic ideas and technocratic economic governance. It is also a book about the changing political economy of British capitalism's relationship to the European and wider global economies. It focuses on the creation in 2010 and subsequent operation of the independent body created to oversee fiscal rectitude in Britain, the Office for Budget Responsibility (OBR). More broadly, it analyses the politics of economic management of the UK's uncertain trajectory, and of British capitalism's restructuring in the 2010s and 2020s in the face of the upheavals of the global financial crisis (GFC), Brexit and COVID. A focus on the intersection between expert economic opinion of the OBR as UK's fiscal watchdog, and the political economy of British capitalism's evolution through and after Brexit, animates a framework for analysing the politics of technocratic economic governance. The technocratic vision of independent fiscal councils fails to grasp a core political economy insight: that economic knowledge and narratives are political and social constructs. The book unpacks the competing constructions of economic reason that underpin models of British capitalism, and through that inform expert economic assessment of the UK economy. It also underlines how contestable political economic assumptions undergird visions of Britain's international economic relations. These were all brought to the fore in economic policy debates about Britain's place in the world, which in the 2010s centred on Brexit. This book analyses OBR forecasting and fiscal oversight in that broader political context, rather than as a narrowly technical pursuit.