The Chagos Islands are a group of around 60 islands, officially called the British Indian Ocean Territory. They are almost 6,000 miles from the UK, but their location makes them strategically important. The largest island, Diego Garcia, is home to a joint UK–US military base, one of the most important Western military facilities outside Europe. It sits in the middle of the Indian Ocean, within range of the Middle East, East Africa, South Asia and the shipping lanes that link the Gulf to Asia. The base has a runway long enough for long-range bombers, a deep-water harbour, and satellite and communications facilities. It was used for operations in Afghanistan and Iraq, and more recently against the Houthis and Iran. With China’s navy increasingly active in the Indian Ocean, many in Washington and London now value Diego Garcia even more.
The UK and Mauritius have disputed sovereignty over the islands for years, and the dispute has been fought in both UK and international courts. It goes back to 1965, when Britain separated the Chagos Islands from Mauritius three years before Mauritian independence. Mauritius says it only agreed under pressure, as the price of independence. Between 1967 and 1973, Britain removed the islands’ population of around 1,500 to 2,000 Chagossians so that the US base could be built. Most were sent to Mauritius and the Seychelles, and many ended up living in poverty.
Several international rulings have gone against the UK. The most important came in 2019, when the International Court of Justice gave an advisory opinion, by 13 votes to 1, that Britain had not lawfully completed the decolonisation of Mauritius. It said Britain should end its administration of the islands “as rapidly as possible”. The UN General Assembly then voted by 116 to 6 to demand that Britain withdraw.
In 2025, under heavy international pressure, the UK Government agreed a deal to hand sovereignty of the islands to Mauritius. It was fiercely contested at home. The Conservatives argued that it gave away British territory and put a vital military base at risk, especially given Mauritius’s close ties with China. They also objected to British taxpayers paying to lease back a base on land the UK already controlled, and said the Chagossians had not been properly consulted. Kemi Badenoch pledged that a future Conservative government would scrap the deal. Labour replied that negotiations had begun under the Conservatives in 2022, and that without a settlement the base’s legal future would be uncertain.
Under the deal, Britain would keep the base on Diego Garcia through a 99-year lease. The deal would cost around £101 million a year on average, or about £3.4 billion over its lifetime in today’s money. The Government’s real problem, though, was Donald Trump. In early 2025 he said he was inclined to go along with the deal. By January 2026 he had turned against it, calling it “an act of GREAT STUPIDITY” on social media. In February he wrote directly to Starmer: “DO NOT GIVE AWAY DIEGO GARCIA!” He said Starmer was “making a big mistake by entering a 100 Year Lease”. He warned that the US might need Diego Garcia to head off a possible attack from Iran, and said he reserved the right to “militarily secure” the base. In April the deal was paused. Last week, the Defence Secretary, Wes Streeting, confirmed it was under review and said Britain would not make any lease payments to Mauritius for now.
The announcement came as Andy Burnham met Trump for the first time, at the UN General Assembly in New York. Trump again called it a “terrible deal” and said he expected Britain to reconsider. Streeting said the President’s comments were “not news to us” but gave “absolute clarity” that his position was not changing. He still rejected Conservative calls to bin the deal entirely.
Britain’s dilemma can be framed as a choice between liberal and realist approaches. From a liberal perspective, international law says Britain’s current position is unlawful, and the deal lets it comply while keeping most of the strategic benefits. Britain also regularly calls for a “rules-based international order” and criticises Russia and China for ignoring international courts. If it ignored the ICJ itself, it would look hypocritical and weaken its moral authority.
Realists see it differently. States act on power and national interest, and an advisory opinion does not change that. Diego Garcia’s location makes it one of the most valuable assets Britain brings to its relationship with the United States. With competition with China growing and the Middle East unstable, realists argue that giving up sovereignty over such a location would be a serious mistake. Letting the issue damage the “special relationship” would be worse still.
Burnham’s government has no easy option. If it keeps the deal, it risks a lasting row with the Trump administration. If it scraps the deal, Britain will be defying international law and will probably face more legal action from Mauritius. The review gives the government time. Whether that time helps may depend more on Washington and Port Louis than on anything decided in London.