In order to answer the statement of whether constitutionalism is something that is far more important than the idea of legality in the United Kingdom, in this essay, I will be outlining the definition and characteristics of British constitution, the doctrine of constitutionalism, idea or principle of legality, rule of law, separation of power and prerogative power. Therefore, I will conduct the existence of the constitution, the current logic based upon it and the doctrine of constitutionalism in