The UK government has agreed to recognise the sovereignty of Mauritius over the Chagos Archipelago, a colonial possession of the UK in the Indian Ocean, and to take a long lease from Mauritius of Diego Garcia, its largest island, and home to a US military base. The UK government maintains that its agreement with Mauritius will allow the Diego Garcia Base to maintain its important strategic role in the future, but critics in the UK and the US disagree. They insist that it is a mistake for the UK to give up its sovereignty over the Archipelago, because its agreement with Mauritius could open the door to Chinese spy ships, a Chinese base on one of the Chagos Islands, restrictions on nuclear weapons on Diego Garcia, and compulsory inspections to check for compliance. But critics overlook or understate the actual provisions of the agreement, which allow the UK and the US unrestricted rights to patrol the Chagos Archipelago, give the UK a veto over spy ships, foreign bases and even civilian development, and allow the presence of nuclear weapons, without requiring compulsory inspections. While the ultimate guarantor of the security of the US Base on Diego Garcia is US hard power, legitimacy still matters. Through the Chagos agreement the UK offers a legitimacy for the US presence on Diego Garcia that it has lacked to date, in the eyes of adversaries and allies alike.

E-International Relations is free to read. We rely on reader support to make this possible.

The UK’s agreement with Mauritius recognises the latter’s sovereignty over the British Indian Ocean Territory, also known as the Chagos Archipelago, or Chagos Islands. It includes a 99-year lease to the UK of Diego Garcia, which is intended to ensure business as usual for its strategically important UK/US base. There is a price to be paid for this; over the 99 year period, the UK will pay Mauritius a total of around £3.4 billion in 2025/26 prices.

President Trump commented recently that the deal is “an act of great stupidity.” This appeared to cast doubt on the support given to the agreement by the White House and the State Department in May 2025, and led to a pause in the parliamentary process in the UK for its ratification. Then President Trump seemed to be backing the agreement once more, and the State Department repeated its endorsement, but the very next day President Trump took to social media to attack the agreement again, saying : "Prime Minister Starmer should not lose control, for any reason, of Diego Garcia, by entering a tenuous, at best,100 Year Lease." The UK government was reported as planning to resume the ratification process after the State Department’s published re-endorsement, but as having paused for further thought after President Trump’s latest comments. The present writer suggested recently that an extended pause in the ratification process would be the least bad response the UK government could make if President Trump expressed serious opposition to the agreement going forward, and that a take-over of the Chagos Islands by President Trump could not be ruled out.

President Trump’s suggestion that committing to the Chagos agreement would mean losing control of Diego Garcia reflects criticisms made both in the UK and the US to the effect that the agreement would be a poor substitute for UK sovereignty, would weaken the effectiveness of the US base, and cede a strategic advantage to China. But these criticisms gloss over generally-perceived weaknesses in the UK’s claim to sovereignty, the actual substance of the Chagos agreement, and the political context which led to it being negotiated in the first place.

The starting point for analysis is the fact that virtually every national government in the world regards the UK’s past claim to sovereignty over the Chagos Islands as having been overtaken by the modern law and practice of decolonisation. In an earlier article the present writer discussed events which led to allies in NATO and the Indo-Pacific refusing to back the UK’s claim to sovereignty over the Chagos Islands in a United Nations vote on the issue in 2019. Only three countries, all led by acolytes of President Trump at the time, voted with the UK and the US. That was the turning of the political tide that led to Conservative Prime Minister Rishi Sunak starting talks with Mauritius in 2022 on sovereignty over the Chagos Archipelago and the future of the US Base on Diego Garcia, and to Sunak’s Labour successor Sir Keir Starmer signing an agreement on those issues with Mauritius in May 2025. Opponents of the deal say that it is a mistake for the UK to give up its sovereignty because........

© E-International