Chagos Islands: Why has U.K. handed it over to Mauritius after 50 years?

Story so far: Mauritius won a strategic victory on May 22, 2025, when the United Kingdom (U.K.) officially handed over sovereignty of the Chagos Islands after finalising the political treaty agreed to in October last year. Under the deal, the important naval and bomber base on Diego Garcia — one of the archipelago’s largest island, operated by U.S. forces, will be leased by the U.K. from Mauritius which will maintain sovereignty over the region. 

Terming the deal as vital to British security, Mr. Starmer said that it was the only way to maintain the naval base’s long-term future. He added that if U.K. had not agreed to the deal, the legal challenges mounted by Mauritius would open avenues to China or any other nation set up their own bases on the outer islands or carry out joint exercises near its base. Mauritius has agreed to initially lease Diego Garcia to the U.K. for £101 million a year for 99 years. 

The British are letting go of the islands after 50 years, after initially buying it for £3 million in 1968.

History of Chagos islands

In 1793, the French established coconut plantations in the islands off approximately 1000 km from Maldives. A set of eight atolls i.e. ring-shaped islands, totalling sixty islands — Peros, Salomon, Nelsons, Three Brothers, Eagle, Danger, Egmont and Diego Garcia along with Mauritius and Seychelles were handed over to the British empire in 1814. Initially, the islands were inhabited by the African slave workers and Asian natives who spoke French-based languages. However, the population changed as contractors from Mauritius and Seychelles arrived in the 1950s and 1960s to work, but not own lands or houses. 

In 1965, these islands were constituted as the British Indian Ocean Territory (BIOT) along with the islands of Aldabra, Desroches and Farquhar — which were later ceded to Seychelles during its independence in June 1976. As the British empire began shrinking, U.K. envisaged the use of Chagos island as a military base. Roping in the United States (U.S.) as a partner in 1967, the U.K. allowed the U.S. to use Diego Garcia for defence purposes initially for 50 years and the agreement would remain in force for further twenty years, (beyond 2016) unless terminated by either nation. 

A year later, on March 12, 1968, Mauritius gained freedom from the British and U.K paid a £3 million grant in recognition of the detachment of the Chagos Archipelago from Mauritius and amongst other legally binding undertakings. Between 1968 to 1973, plantations across the islands were shut and the BIOT administration forcibly removed the inhabitants to make way for the military base in Diego Garcia. Inhabitants have been exiled from the island giving them a choice to move either to Mauritius or Seychelles. In 1971, BIOT passed an ordinance making it unlawful for a person to enter or remain in BIOT without a permit and allowed those remaining to be removed. 

Estimated to have exiled around 10,000 Chagossians, the British paid £6,50,000 in the 1970s and a further £4 million in 1980s to Mauritius for resettlement. In 2002, the U.K. changed the British Nationality law allowing Chagossians who had BIOT citizenship to automatically become British citizens. Currently, a small community of Chagossians reside in Crawley, Sussex, and another in Manchester, still fighting for their right to return to their native land.

Who is fighting for sovereignty of Chagos?

Since its independence, Mauritius has claimed sovereignty over Chagos, claiming that the U.K. was in violation of United Nations (UN) resolutions which banned dismemberment of colonies before independence. It claimed that the 1968 agreement which allowed Chagos’ detachment was signed in exchange for Mauritius’ freedom. Over several round of talks, the U.K. and Mauritius have been trying to resolve the issue but did not make much progress till last year. 

In 2010, U.K. further asserted its sovereignty over BIOT by declaring the area as a ‘Marine Protected Area’ (MPA). Citing the presence of 220 species coral, 855 species of fish and 355 species of molluscs in BIOT, U.K declared an area of 640,000 km² as a ‘no-take’ — banning all commercial fishing and extractive activities. However, Mauritius challenged this move in the Permanent Court of Arbitration and the court ruled in 2015 that the declaration of MPA was not compatible with U.K’s obligations under the UN convention on the Law of the Sea. It also held that Mauritius held rights to legally fish in the waters surrounding Chagos, reap benefits from any oil discovered in that area and that the islands would be eventually returned to Mauritius after UK no longer needed for defence purposes. However, the court refused to settle the sovereignty issue between the two nations, claiming it did not have jurisdiction. 

Mauritius’ efforts were boosted when the UN General Assembly passed a resolution (94 in favour to 15 against, 65 abstained) urging the International Court of Justice (ICJ) to render an advisory opinion on the legal consequences of Chagos’ separation from Mauritius during its independence, questioning if the ‘decolonisation’ was done lawfully.

On February 25, 2019, the ICJ found that decolonisation of Mauritius was not lawfully completed following the separation of Chagos and that the U.K was obligated to end its administration of Chagos as rapidly as possible. It also ordered all UN member states to co-operate with completing Mauritius’ decolonisation lawfully.

What does the U.K-Mauritius deal cover?

Five years later, on October 3, 2024, the U.K and Mauritius announced a deal after eleven rounds of negotiations since 2022, marking an end to the ‘total process of decolonisation’. Under the new deal, UK will handover Chagos’ sovereignty to Mauritius and lease the use of Diego Garcia for 99 years at an average cost of £101 million per year. For the first three years, U.K. will pay £165m annually; for year four to thirteen it will pay £120 million annually. After that, payments will be indexed to inflation, reported BBC. 

The use of the military base in Diego Garcia has been signed off by the UK’s ‘Five Eyes’ allies – US, Canada, Australia and New Zealand and the running costs of the base will be footed by US. A 24-mile buffer around Diego Garcia has been agreed to where nothing can be built without U.K. consent. Moreover, foreign militaries and civilian forces are barred from all of Chagos with U.K. retaining a power to veto any access to the islands.  

The U.K. will also set up a £40m trust fund to support Chagossians. However, Mauritius will not be allowed to resettle Diego Garcia inspite of having sovereign control over it. The agreement also shuts down any possibility of the Indian Ocean being used as a dangerous illegal migration route to the U.K., with Mauritius taking responsibility for any future arrivals. This treaty comes into effect only after it is approved by both the U.K. and Mauritian parliaments. 

Two Chagossians, born in Diego Garcia, challenged the deal, claiming that they wanted to return to the islands and not Mauritius or Seychelles. While a court injunction was granted, temporarily blocking the deal, the U.K. High Court dismissed the challenge.

Why is there opposition to the deal?

Mr. Starmer’s prime opposition — the Conservative party, has slammed the deal due to apprehensions of handing over sovereignty of a military base to Mauritius — a close ally of China. Conservatives have also critiqued the a “net cost” of £3.4bn after adjusting for inflation, which this deal will add to the British exchequer.

What is India’s role in the deal?

India, a former British colony itself, played a quiet and important role in backing Mauritius’ position to ‘do away with the last vestiges of decolonisation’, reported The Hindu. Encouraging both U.K and Mauritius to negotiate with an open mind towards mutually beneficial outcomes, India strived for long term security in the Indian Ocean region. Both India and US were acknowledged by the two parties for their “full support and assistance” in reaching to the political agreement. 

The Ministry of External Affairs (MEA) issued a statement welcoming the deal, affirming its support of Mauritius’s “legitimate claim” over the Chagos Archipelago in keeping with its principled position on “decolonisation, respect for sovereignty, and the territorial integrity of nations”. It added that India remains committed to working closely with Mauritius and other like-minded countries to strengthen maritime security, peace and prosperity in the Indian Ocean.