British Indian Ocean Territory

The British Indian Ocean Territory (BIOT) is a British Overseas Territory situated in the Indian Ocean. The territory comprises the seven atolls of the Chagos Archipelago with over 1,000 individual islands, many very small, amounting to a total land area of 60 square kilometres (23 square miles). The largest and most southerly island is Diego Garcia, 27 square kilometres (10 square miles), the site of a Joint Military Facility of the United Kingdom and the United States. Official administration is remote from London, though the local capital is often regarded as being on Diego Garcia.

Mauritius claims that the British government separated the Chagos Archipelago from Mauritius, creating a new colony, the British Indian Ocean Territory (BIOT). However, this is disputed by the United Kingdom, which insists that the Chagos Islands had no historical or cultural ties to Mauritius, and that they were only governed during the colonial period from Mauritius (2191 km or 1361 miles away) as an administrative convenience as had been the practice when the islands were under French rule. Mauritius further claims that, to avoid accountability to the United Nations for its continued colonial rule, the UK has falsely claimed that the Chagos had no permanent population.

Since 1971, the only people allowed to live on the Chagos Islands have been British and United States military personnel, and associated contractors, who collectively number around 3,000 (2018 figures). The forced removal of Chagossians from the Chagos Archipelago occurred between 1968 and 1973. The Chagossians, then numbering about 2,000 people, were expelled by the British government to Mauritius and Seychelles, even from the outlying islands far away from the military base on Diego Garcia. Despite calls from numerous human rights organisations, the British government has repeatedly denied Chagossians the right of return. In 2026, four Chagossians returned to Île du Coin in an attempt to reestablish a permanent settlement, without seeking government permission; their effort is being challenged in court.

Since the 1980s, the Government of Mauritius has sought to gain control over the Chagos Archipelago, which was separated from the then Crown Colony of Mauritius by the UK in 1965 to form the British Indian Ocean Territory. A 2019 advisory opinion of the International Court of Justice called for the islands to be given to Mauritius. Both the United Nations General Assembly and the International Tribunal for the Law of the Sea subsequently reached similar decisions. Negotiations between the UK and Mauritius began in 2022, and culminated in 2024 understanding that the UK would cede the territory to Mauritius for possible resettlement while retaining the joint US-UK military base on Diego Garcia.

A treaty was signed on 22 May 2025 that would formally transfer sovereignty of the territory to Mauritius once ratified, with the Diego Garcia military base remaining under British control during a 99-year lease. Following backlash from United States President Donald Trump in 2026, ratification has been suspended. The UN Committee on the Elimination of Racial Discrimination has expressed "deep concern" at the terms of the deal.