This study focuses on Britain's relations with the Zollverein - the German Customs Union - in its later period. It includes Britain's reaction to the plans for commercial unity drawn up at Frankfurt in 1848 and whether it contributed to the failure of the revolution. It looks at the tumultuous Zollverein conferences of the 1850s, and the rumours of British spies attempting to sabotage further economic integration and decimate German industry. It reveals Britain's important role in Bismarck's thrust for economic leadership in the Zollverein crisis of the 1860s. The discussion is firmly set in the context of British Free Trade and illuminates the way in which decision-making institutions in London and representatives on the ground in the German states operated. By careful comparison of British and German documents, it produces a picture of Britain's policy markedly different from the way it was perceived in the German states, and revises many common assumptions about Britain's Zollverein policy.