Perpetuating Britain's controversial administration of the Chagos Archipelago (BIOT-British Indian Ocean Territory) raises questions about the UK's commitment to the rules-based order and international law. This interdisciplinary article examines British administration of the Chagos Archipelago by taking a legal-international relations perspective. It provides an overview to the rules-based order concept and its relation with international law, briefly examines the Territory's history, and outlines how BIOT violates the principles enshrined in the rules-based order concept, specifically promotion of self-determination, prohibition of forced displacement and respect for international institutions. This study is significant due to its timing-set in a period of increased international pressure on the United Kingdom to cede sovereignty of the Chagos Archipelago to Mauritius-and also significant in a period of increased rules-based order strain throughout the Indo-Pacific. This article argues that, despite Britain's assertion that it is a champion of the rules-based order, of which international law is a component, continued British administration of the Chagos Archipelago is in contravention of both. In an era of rules-based order strain, British BIOT policy provides fertile ground to criticisms of its foreign policy and international law selectivity and double standards.