The decision was unexpected and controversial, despite lengthy legal proceedings before international organisations at the initiative of Mauritius. The decision to cede the archipelago was most likely taken with the aim in mind of improving Britain’s image in the countries of the Global South. In doing so, Keir Starmer’s government broke with the previous line of argumentation regarding the status of the archipelago, which emphasised the needs of British security policy and stressed the non-legally binding (consultative) nature of decisions by international organisations favourable to Mauritius. The controversy over the cession was heightened by the lack of public debate during and after the recent election campaign in the House of Commons (it was announced during a recess of several weeks) and the omission of representatives of the Chagossians (islanders displaced in the 1970s) from working out an agreement with Mauritius. The cession will also affect the British Strategic Defence Review, which began in July this year.

The Importance of the Chagos Islands to British and U.S. Global Strategy

Following their separation with compensation from Mauritius in 1965 (then a British colony) to form the British Indian Ocean Territory (BIOT),  a military base began to be constructed on Diego Garcia, the largest atoll within the archipelago. Although it remained British-owned, from the beginning its main user was the United States, which in 2016 extended the agreement for its use for 20 years.

The base has infrastructure to support U.S. strategic and naval aviation (including the largest aircraft, e.g., B-52, B-1, B-2, E-3 Sentry, P-8 Poseidon). Maritime infrastructure includes permanent fuel, equipment and armament storage, and cargo-handling facilities. The base has a sheltered anchorage for the stationing of ships (including the most important types, such as aircraft carriers and nuclear-powered submarines) and support via floating docks, as well as the prepositioning of cargo ships with military supplies to support operations in the maritime, air, and land domains. The forces based at Diego Garcia can control in peacetime and wartime the most important sea and air routes across the Indian Ocean between Africa, the Middle East (and further Europe), and South Asia, as well as the passages to the Pacific Ocean. Consequently, the base is crucial to the continued maintenance by the U.S. (and, if necessary, the UK) of a global power-projection capability. It has been used by U.S. forces in the 21^st century for missions in Afghanistan and Iraq, among others.

The Prospective Status of the Chagos Islands

The political agreement of 3 October has a framework character and the detailed and legally binding arrangements will be contained in a treaty. The agreement provides for the transfer of sovereignty over the archipelago to Mauritius, with the UK reserving the right to exercise it for 99 years over the Diego Garcia atoll (which would extend the use of the base by U.S. forces), in return for lease payments to Mauritius. The agreement also provides for the right of Chagossians to return to the archipelago.

Previously, full sovereignty over the BIOT allowed the UK (and consequently the U.S.) not only to use the Diego Garcia base but also to prevent other countries from developing their own military or reconnaissance infrastructure in the archipelago (in which China and India, among others, have shown interest). The new status leaves open the question of the use of the remaining atolls of the archipelago by third countries in agreement with Mauritius. The status of the Exclusive Economic Zone (EEZ) around the archipelago remains unclear. The loss of control of the EEZ and territorial waters (excluding the 12 nautical mile wide strip around Diego Garcia) by the UK (and consequently the U.S.) may make it easier for third countries to carry out intelligence surveillance of the base and, in the event of inadequate enforcement by Mauritius (which is more than 2,000 km from the Chagos Islands), also make it more difficult to combat piracy and illegal fishing (currently the waters around the archipelago are the world’s largest marine protected area).

Legal and International Implications

One of the most controversial aspects of the cession from a British policy perspective is the omission of the Chagossians from the decision-making process. Since independent Mauritius had never exercised sovereignty over the Chagos Islands, its claim was based, first, on the legal legacy of the colonial era and, second, on the representation of the collective rights of the Chagossians. The Starmer government’s decision sets a precedent challenging the argument consistently promoted by various British governments since the 1960s regarding the status of several key British Overseas Territories (BOTs) with disputed status, especially the Falkland Islands (Las Malvinas) and Gibraltar. To date, the UK has argued that the process of decolonising such territories should be at the request of the local population (hence the referendums in Gibraltar in 2002 and the Falkland Islands in 2013, which confirmed their status as BOTs), rather than based on the historical rights of third countries to the territory.

In the case of the Chagossians, the British government omitted, on the one hand, consultation with that group (some of whom have British citizenship and express a desire to maintain the islands’ BOT status after regaining their right of return to the archipelago), while on the other hand, it factually recognised the historical claims of Mauritius and its status as the main representative of the Chagossians. As a result, this precedent could strengthen Spain’s position in the Gibraltar dispute or Argentina’s position in relation to the Falkland Islands as states claiming historic rights to the disputed territories against the position of the local population. The precedent is also significant from the point of view of the final status of British bases in Cyprus, often shared with the U.S. (e.g., used in defence of Israel against Iranian missile attacks). The decision to cede the archipelago did not prevent Commonwealth states from making claims against the UK at the Samoa Summit on 25 October for reparations for historical colonisation and slavery, which were rejected by Lammy and Starmer.

Conclusions and Outlook

The decision to change the status of the Chagos Islands became an unexpected factor affecting the Strategic Defence Review launched by the New Labour government in July this year. The Starmer government has demonstrated a willingness to fundamentally alter the UK’s previous legal and political reasoning in relation to disputed territories of strategic importance, suggesting a much broader scope for the review of the UK’s 2021-23 global strategy than Labour had previously announced. While the future model and timeframe for the use of the Diego Garcia base will be decided by the treaty with Mauritius, historical precedents (e.g., Singapore, Malta) indicate that the exploitation of UK bases of comparable status has often ended before the expiry of the lease. The cession is also likely to be the subject of analysis by the upcoming Trump administration in the near future.

From the point of view of Poland and other U.S. allies in Europe and East Asia, Diego Garcia represents a difficult-to-replace staging base for the redeployment of U.S. (and British) tactical aviation and smaller ships between the Mediterranean and Indo-Pacific areas. Undermining the base’s current operating model would therefore reduce the strategic mobility of U.S. forces, lead to stronger dispersion, and make it more difficult to concentrate them in Europe if necessary. Ultimately, it would force the countries on NATO’s Eastern Flank to field new forces of their own. The manner in which the decision was taken could also negatively affect the status of Gibraltar and the bases in Cyprus, resulting in new tensions between the UK and the European Union, or the need to maintain additional British forces in the Falkland Islands.