Putting the Cart before the Horse?
The United Kingdom's Recognition of Mauritius' Sovereignty over the Chagos Islands Revisited
On 3rd October 2024, Mauritius and the United Kingdom published a Joint Statement on both governments’ websites (UK.gov and govmu.org). This political agreement addresses the sovereignty of the Chagos Islands, five years after the International Court of Justice (ICJ) issued an advisory opinion declaring the UK’s administration of the archipelago a violation of international law. It sets the stage for a treaty in which the UK will recognize Mauritius’ sovereignty over the Chagos Islands in exchange for retaining sovereign rights over Diego Garcia for 99 years, renewable thereafter.
Maneesh Gobin, former Minister of Foreign Affairs of Mauritius, described the event on X (formerly Twitter) as “[a] day to remember. A day to commemorate full sovereignty of the Republic of Mauritius over the entirety of its territory.” However, the use of the terms ‘full sovereignty’ merits scrutiny. Two critical issues arise: first, that the treaty formalizing the recognition of sovereignty has not yet been finalized and second, that the proposed treaty’s terms may raise significant concerns regarding the principle of self-determination.
Historical Background and Legal Developments
The Chagos archipelago was separated from Mauritius in the 1960s during its decolonization process. This separation served British interests, as the UK sought to lease Diego Garcia – the largest inhabitable island in the archipelago – to the United States for the establishment of a military base. As part of this arrangement, the UK expelled the Chagossians from their homeland.
Following the establishment of the base, the UK met all of Mauritius’ and the Chagossians’ attempts to challenge its actions with diplomatic silence, amending its optional clause of compulsory jurisdiction to exclude sovereignty disputes over the Chagos Islands.
In the last decade, Mauritius started to resort to ‘judicial strategies’ to obtain changes, starting with the 2015 Chagos Marine Protected Area Arbitration. The arbitral award avoided direct territorial sovereignty issues to focus on questions relating to the law of the sea, but upheld Mauritius’ fishing rights in the area. Following this, the ICJ’s 2019 advisory opinion marked a turning point as it affirmed that the process of decolonization had not been lawfully completed, and that Mauritius is sovereign over the archipelago. Though non-binding, this opinion carried significant weight and influenced subsequent rulings, such as the arbitral award in the maritime boundary dispute between Mauritius and the Maldives. The Special Chamber of the International Tribunal for the Law of the Sea deemed the ICJ’s opinion an ‘authoritative statement of the law’ (para. 205-206) and thus confirmed that, on this basis, Mauritius must be considered sovereign.
The Joint Statement and Its Implications
Several factors played into the UK’s motivation to negotiate. The failure to respect the ICJ’s advisory opinion attracted international criticism and weakened the UK’s position on international political issues such as the Ukraine war and the South China Sea dispute. The looming threat of a binding judicial ruling, coupled with pressure from the Biden administration pushed the UK to negotiate in 2022, leading to a first concrete result in the Joint Statement.
Substantial financial compensation is also under negotiation, likely a key factor in Mauritius’ willingness to engage in the deal. However, recognition remains contingent on the treaty’s conclusion, leaving the sovereignty question unresolved for now.
While former US President Biden celebrated the agreement, the treaty’s future faces political uncertainty. President Trump and his Secretary of State, Marco Rubio, have voiced strong opposition, citing risks to US national security and potential Chinese influence in Mauritius. Moreover, Mauritius’ New Prime Minister, Navin Ramgoolam, has also expressed reservations about the deal. He has called for an independent review of the first draft and is said to have send a fresh proposal to the UK, likely considering a larger sum of money than originally planned. This political volatility raises an important question: if the treaty collapses, does the Joint Statement already impose legal obligations on the parties?
The Joint Statement as a Legal Commitment
It could be argued that the Joint Statement constitutes a collective unilateral act under international law, binding both parties to their expressed commitments. However, unilateral acts typically lack mutual concessions, whereas this statement explicitly involves a quid pro quo: UK recognition of sovereignty in exchange for the exercise of sovereign rights over Diego Garcia.
Moreover, the ICJ’s Nuclear Tests case clarified that unilateral declarations create binding obligations only when States intend to be bound by them (para. 46). Yet the Joint Statement expressly states that its terms are ‘subject to the finalization of a treaty’, signaling that both parties intended only the future treaty, not the statement itself, to carry binding force. Moreover, it is written that the UK ‘will agree that Mauritius is sovereign’, in exchange for the transfer of sovereign rights. The use of the future tense and the conditionality implied by this reciprocal concession means that none of these two States intended to be bound individually by way of a unilateral act. That said, the statement could still have legal consequences. The repeated affirmations of intent to conclude a treaty – including in another Joint Statement of 20 December 2024 – may create obligations, of result or of means, under the doctrine of estoppel. Under this doctrine, a State that has established a certain representation through its actions, on which another State has relied, is prevented from later altering that conduct if it would cause a disadvantage to the other party.
The Respect of the Right to Self-Determination
A significant flaw of the Joint Statement lies in its conditional recognition of sovereignty, to which the UK is bound by virtue of international law. The UK’s insistence on retaining rights over Diego Garcia maintains the status quo by prolonging its control over the island. This arrangement raises questions about whether an administering power can condition recognition of sovereignty on such concessions, thereby maintaining a de facto administration.
While States are generally free to transfer sovereign rights, based on the free disposition of the territorial title principle, the situation becomes complex when viewed through the lens of self-determination. The ICJ has recognized the right of self-determination as a peremptory norm of international law (jus cogens) in its 2024 advisory opinion regarding the Palestine occupation (para. 233). In principle, a State cannot relieve itself of the obligations imposed on it by a norm of jus cogens vis-à-vis another State, even by treaty, i.e. with the consent of that other State. Nor, therefore, can a right derived from a peremptory norm be waived (the only case in point being the right to self-determination). In addition, under Article 53 of the Vienna Convention on the Law of Treaties (VCLT), treaties violating peremptory norms are void.
Precisely, however, transferring sovereign rights could be interpreted as an exercise of self-determination rather than a violation of it. Indeed, since a state cannot cede part of a territory over which it has no sovereignty – under the maxim ‘Nemo plus juris ad alium transferre potest quam ipse habet’ (no one can transfer more rights than they themselves possess) –, it follows a contrario that only a state with a sovereign title can do so. This means that cession is an attribute of sovereignty. Yet, the exercise of self-determination is an exercise of sovereignty, and sovereignty over a territory implies the right to freely dispose of it, including the right to cede it. This creates a paradox: while the State cannot renounce the people’s right to self-determination, ceding sovereign rights could itself be an expression of that right.
In this case, the proposed treaty does not appear to violate self-determination outright. However, it perpetuates a problematic status quo, leaving questions about the legitimacy of the conditional recognition of sovereignty unresolved.
International Human Rights Law and the Chagossians
The lack of consultation of the Chagossians raises questions about the legitimacy and legality of the future treaty. Under the right to self-determination, however, the opinion of the Chagossians is irrelevant. They are considered as one with the Mauritians, because their separation from the rest of the people was a violation of Mauritius’ territorial integrity. Yet the people of Mauritius, which includes the Chagossians, would be considered to have expressed itself, through the voice of their legal representatives, in case of the conclusion of a treaty.
However, the question may arise of the respect of international human rights law, which does take the Chagossian people into account (ICJ, 2019 Advisory opinion, para. 181). The advisory opinion emphasized the need to consider the Chagossians, who were forcibly displaced during the establishment of the Diego Garcia military base. In the Chagos Islanders case, the ECtHR declared a case brought by Chagossians inadmissible, stating that they had already obtained reparation in the UK’s national legal order, for the harm caused by the removal from the islands. It seems then that no other reparation is possible for this initial violation of the Chagossians’ rights. Nonetheless, the UK maintaining control of Diego Garcia and denying a right to return to the Chagossians may be seen as causing a new harm. For example, article 13 (2) UDHR reads as follows: ‘Everyone has the right to leave any country, including his own, and to return to his country’, and article 12 (4) ICCPR as ‘No one shall be arbitrarily deprived of the right to enter his own country’. The Chagossians could then seek to obtain compensation before an international human rights body such as the Human Rights Committee.
Conclusion
The Joint Statement represents a significant step in addressing the sovereignty of Mauritius on the Chagos Islands, but it seems to be raising as many questions as it answers. While the agreement does not appear to violate the peremptory norm that is the right to self-determination directly, its conditional approach to the recognition of Mauritius’ sovereignty and its failure to address the rights of the Chagossians could as well be considered violations of international law.
Ultimately, the Joint Statement exemplifies the complexities of decolonization in contemporary international law. Whether the future treaty will bring closure to this decades-long dispute or simply perpetuate existing injustices remains uncertain.

Jérémy Mota has worked as a PhD Student in Public International Law at Paris 1 Panthéon-Sorbonne University for the last three years. He is also a teaching assistant in International Economic Law (WTO Law) and Public International Law. His PhD thesis is about “The Adaptation of International Law on Procedure and Evidence to Environmental Disputes”.