Constitutional supremacy and parliamentary sovereignty offer two different answers to a question common to every constitutional democracy: which organ should exercise final control over the making and validity of law? This paper examines how the United Kingdom and India answer that question through the relationship between legislative power and judicial review. The research problem is whether a sovereign Parliament and a constitutionally limited Parliament differ in kind or only in degree when courts review legislative and executive action. The study adopts a doctrinal and comparative method and analyses constitutional and statutory texts and the leading judgments of both jurisdictions, supported by secondary literature. On the UK side, it examines the Diceyan doctrine, the Human Rights Act 1998, R (Factortame Ltd) v Secretary of State for Transport, R (Jackson) v Attorney General and the post-Brexit restoration of legislative supremacy. On the Indian side, it examines Kesavananda Bharati v State of Kerala, Indira Nehru Gandhi v Raj Narain, Minerva Mills Ltd v Union of India and SR Bommai v Union of India. The paper finds that the two systems differ in the remedy available against legislation rather than in the presence of legal limits. Indian courts may invalidate statutes, and even constitutional amendments that damage the basic structure, whereas UK courts may only interpret primary legislation compatibly with Convention rights, declare it incompatible or, during EU membership, disapply it. Both systems nonetheless subject executive power to searching review of legality. The paper concludes that the two models are moving towards a shared constitutionalism of legality expressed through different institutional forms. A closing section considers how each model responds to automated decision-making and to emergency governance.