<p>There is a growing use of Artificial Intelligence (AI) systems in high-stakes environments such as healthcare and transportation, where errors or misuse can lead to serious and potentially irreversible consequences. Existing regulatory frameworks remain fragmented and often inadequate to address the complexity of AI development in these settings. Although ethical principles such as safety, fairness, accountability, transparency and human oversight are widely recognised, their translation into enforceable legal obligations remains uneven across jurisdictions and sectors. The central question addressed in this paper is how AI use in high-stakes environments should be regulated to achieve effective and enforceable obligations. The paper makes four contributions. First, it develops a three-tier Ethics Pyramid, a framework that distinguishes foundational ethical values, second-level governance principles, and third-level operational mechanisms. The framework functions as an allocation model, helping regulators identify which ethical principles should be juridified and at what level of governance this should occur. Second, the paper evaluates regulatory theories, strategies and instruments and argues that a polycentric, multi-layered legal framework is better suited to high-stakes AI governance. Third, it conducts a comparative analysis of high-stakes AI regulation in the UK, the EU, the US and China, alongside a sectoral examination of healthcare, autonomous vehicles, criminal justice and public sector decision-making. The analysis reveals significant variation in regulatory maturity. Fourth, it develops a polycentric, multi-layered legal architecture illustrated through case studies of AI use in UK prisons and autonomous vehicles, highlighting the contrast between fragmented and mature regulatory regimes.</p>