In Westminster systems, governments enjoy strong agenda-setting powers but are accountable to an inquisitorial opposition. This article provides insights into the origins of this arrangement from the British House of Commons, drawing primarily on a new data set of a half million parliamentary speeches. We show that, according to a novel measure we develop, government ministers became more responsive to opposition members of parliament in the same period that the government's agenda power was most conclusively strengthened—roughly, the two decades culminating in Balfour's “railway timetable” of 1902. We argue that this increase in responsiveness helps to explain why opposition members of parliament acceded to reductions in their procedural power. We thus highlight a link between government strength and opposition scrutiny in the historical development of the Westminster system.