On 3 October 2024, following two years of negotiations and judicial proceedings in various fora, the United Kingdom (the “UK”) and the Republic of Mauritius (“Mauritius”) jointly announced that they had reached a political agreement on the exercise of sovereignty over the Chagos Archipelago. The agreement is subject to finalisation of a treaty and supporting legal instruments, which both States have committed to complete as soon as possible.
The Chagos Archipelago consists of a number of coral atolls and islands in the Indian Ocean, with Diego Garcia being the largest island. Between 1814 and 1965, the UK administered the Chagos Archipelago as a dependency of the colony of Mauritius. In November 1965, following meetings with certain Mauritian political leaders, the Mauritius Council of Ministers agreed to detach the Chagos Archipelago from the colony of Mauritius. In return, the UK made certain undertakings to Mauritius, including fishing rights and the return of the Chagos Archipelago when no longer needed for defence purposes. Following the detachment, the Chagossian population was removed and a US military base was installed on Diego Garcia.
In 2010, Mauritius initiated arbitral proceedings against the UK under Annex VII of the UN Convention on the Law of the Sea (“UNCLOS”), challenging the UK’s creation of a marine protected area (“MPA”) earlier that year. In 2015, the tribunal found that it lacked jurisdiction over some of Mauritius’ claims, because the dispute concerned sovereignty over the Chagos Archipelago, not the interpretation or application of UNCLOS. On the merits, the tribunal found that the UK’s undertakings in 1965, which were subsequently repeated, were legally binding. The tribunal ruled that, in establishing a MPA around the Chagos Archipelago, the UK had breached certain obligations under UNCLOS: notably, Article 2(3) (as regards Mauritius’ fishing rights in its territorial sea); Article 56(2) (as regards Mauritius’ rights in its exclusive economic zone); and Article 194(4) (as regards unjustifiable interference with Mauritius’ fishing rights in its territorial sea).
In 2017, the UN General Assembly asked the International Court of Justice (the “ICJ”) to render an advisory opinion on the legal consequences of the separation of the Chagos Archipelago from Mauritius in 1965. In 2019, the ICJ concluded that the Chagos Archipelago’s detachment and incorporation into a new colony (the British Indian Ocean Territory) had been unlawful, and the process of decolonisation of Mauritius had not been lawfully completed in 1968, when Mauritius gained independence. In particular, the ICJ found that the agreement in principle by the Council of Ministers of Mauritius had not reflected “the free and genuine expression of the will of the people concerned” and the UK, as an administering power, was obliged to respect the territorial integrity of Mauritius. As a result, the UK “was under an obligation to bring an end to its administration of the Chagos Archipelago as rapidly as possible, thereby enabling Mauritius to complete the decolonization of its territory in a manner consistent with the right of peoples to self-determination”.
Pursuant to their October 2024 agreement, the UK and Mauritius announced the following: (1) the UK “will agree that Mauritius is sovereign over the Chagos Archipelago, including Diego Garcia”; (2) both States will agree “to the long-term, secure and effective operation of the existing base on Diego Garcia”; (3) for an initial period of 99 years, the UK “will be authorised to exercise with respect to Diego Garcia the sovereign rights and authorities of Mauritius required to ensure the continued operation of the base well into the next century”; (4) Mauritius “will now be free to implement a programme of resettlement on the islands of the Chagos Archipelago, other than Diego Garcia, and the UK will capitalise a new trust fund, as well as separately provide other support, for the benefit of Chagossians”; (5) the UK will provide a package of financial support to Mauritius; and (6) both States “will cooperate on environmental protection, maritime security, combating illegal fishing, irregular migration and drug and people trafficking within the Chagos Archipelago”, which will include establishing a Mauritian MPA.
- The 3 October 2024 joint statement of the UK and Mauritius on the Chagos Archipelago is here.
- The PCA arbitral award in Chagos Marine Protected Area Arbitration (Mauritius v. United Kingdom) is here.
- The ICJ’s advisory opinion on Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 is here.