In a landmark foreign policy move, the United Kingdom has formally agreed to transfer sovereignty of the Chagos Islands to Mauritius, concluding decades of diplomatic and legal dispute. The core of the agreement ensures the UK retains a long-term lease for the strategically vital Diego Garcia atoll, home to a major joint UK-US military facility.
The Path to a Sovereign Transfer
The archipelago, located in the Indian Ocean roughly 1,250 miles north-east of Mauritius, has been a British Overseas Territory since 1814. However, its status has been contested since 1965, when the UK detached it from Mauritius shortly before the latter's independence in 1968. The UK created the British Indian Ocean Territory, and the inhabitants were controversially removed to make way for the military base on Diego Garcia.
Mauritius has persistently claimed sovereignty, a position bolstered by a 2019 advisory opinion from the International Court of Justice (ICJ). The court found the UK's decolonisation of Mauritius was not lawfully completed. This ruling, though non-binding, increased pressure on the UK government. Negotiations began in earnest under former Prime Minister Rishi Sunak in 2022, with the current Labour government, led by Keir Starmer, finalising the treaty with Mauritian Prime Minister Navin Ramgoolam on 22 May 2025.
Terms of the Treaty and Political Backlash
The treaty's key provisions are clear: Mauritius assumes sovereignty over the entire Chagos archipelago, while the UK secures an initial 99-year lease for Diego Garcia, with an option to extend. The financial package for this lease is estimated to have a net present value of £3.4 billion, with an average annual cost of around £101 million.
Prime Minister Starmer defended the deal as a pragmatic necessity, warning that without it, the UK faced the risk of losing legal certainty over the base and potential provisional court orders. The US government, after a review, stated the agreement "secures the long-term, stable, and effective operation" of the Diego Garcia facility.
However, the treaty has sparked significant domestic criticism. Conservative leader Kemi Badenoch labelled it a "surrender", arguing Britain was paying billions to lease back land it owned. The political drama intensified when former US President Donald Trump, in a post on Truth Social, called the plan "an act of great stupidity", linking it to his own ambitions regarding Greenland. This comment came shortly after Starmer publicly criticised Trump's tariff threats over Greenland.
Strategic Implications and the Road Ahead
The primary UK and US strategic objective—preserving the Diego Garcia base—appears secured for the foreseeable century. The base is a critical hub for operations in the Indian Ocean and Middle East. The government argued that the treaty provides the legal clarity needed to prevent other nations, such as China, from establishing a presence on the archipelago's outer islands.
The deal now moves through the UK parliamentary process, where it will face scrutiny from MPs. While it settles a long-standing colonial grievance and aligns the UK with international law, it marks the end of British sovereignty over a territory it has held for over two centuries, a move that continues to divide political opinion in Westminster and beyond.
