Under the Crown, the unifying principle of our constitution is the common law. The common law’s distinctive method has endowed the British state with profoundly beneficial effects.

In this Lecture I will explain why this is so. I will say that by force of the common law, efficacy is allowed but oppression is forbidden to the power of the state; and this is achieved by a benign continuum of developing law. I will tell what is a constitution’s unifying principle, and what is the distinctive method of our constitution’s unifying principle, the common law. I will give two instances of changes wrought without revolution by the common law’s processes; the first concerns the sovereignty of Parliament, the second the judicial review jurisdiction. Then I will explain how Parliament’s legislation only has effect through the methods of the common law. The common law is the interpreter of our statutes, and is the crucible which gives them life. The process of interpretation is intensely coloured by the common law’s insights of substantive principle: reason, fairness and the presumption of liberty. So is the judicial review of executive action. The result is that statute law and government policy are alike delivered to the people through the prism of such principles. This is the gift of the common law, the unifying principle of our constitution. It is the means by which legislature and government are allowed efficacy but forbidden oppression.