Two orthodoxies have been close to the heart of the British state since the mid-19th century. The first is a theory of liberal political economy of free trade and free market transactions; the second is a liberal theory of the constitution of parliamentary sovereignty. Both came to ascendancy in the middle decades of the last century, and both have exerted hegemonic influence in subsequent economic and constitutional discourse. Their rise to hegemony was interconnected as the embryonic liberal democratic state assisted the development of the liberal political economy and, in turn, the latter helped to ensure the stability and expansion of the former. Over the past century, however, both orthodoxies have faced substantial theoretical and empirical challenges, yet, both remain, in diffefent ways, hegemonic. But now, whilst remaining interconnected, the congruity, which was so marked in the mid-19th century, has been replaced by asymmetry whereby free trade and parliamentary sovereignty now appear counterposed. The clearest manifestation of this asymmetry is to be found in the discussion of the European Communities (Amendment) Act in the British House of Commons in 1986 and the implementation of the Single European Act. Why this counterposition has occurred is the major issue to be addressed in this article.