The Chagos Archipelago lies in the middle of the Indian Ocean and comprises 58 islands including Diego Garcia, which houses a major joint British and American military base. The Archipelago has been under continuous British sovereignty since 1814. However, in October 2024, a joint statement was issued by the United Kingdom and Mauritius explaining that the two governments had agreed to draft a new treaty which will provide that the “United Kingdom will agree that Mauritius is sovereign over the Chagos Archipelago, including Diego Garcia.”

As the author has previously explained, the intended surrender of the Chagos Archipelago would represent a major strategic blow to Western security. Moreover, the plan offers no discernible benefit to the British people or to the Chagossian Islanders, many of whom have come out in protest against it. In practice, the UK seems to be making this concession based on fear of a negative future court judgment, with the Foreign Secretary opining that “a binding [judgment] against the UK seemed inevitable.” However, the source of this putative future judgment has not been specified. Surely, if any court with the ability to produce a binding judgment had been available, Mauritius would have already availed itself of that court.

Instead, the legal position of the British Government should be based on existing legal circumstances. As this article will show, there is no binding legal judgment compelling the UK to relinquish sovereignty of the Chagos Archipelago. The adverse statements rendered by the International Court of Justice, the United Nations General Assembly and the International Tribunal for the Law of the Sea were respectively: (i) non-binding legal advice, (ii) political assertion and (iii) a judgment on the territorial boundary between other States (namely Mauritius and the Maldives). The result is that the UK is not bound by any of their terms.

International Court of Justice advisory opinion (2019)

In 2019, the ICJ rendered an Advisory Opinion on the legal status of the Chagos Archipelago. The opinion had three main conclusions. First, “the process of decolonization of Mauritius was not lawfully completed when Mauritius acceded to independence in 1968” (paragraph 174). Second, “it follows that the United Kingdom’s continued administration of the Chagos Archipelago constitutes a wrongful act entailing the international responsibility of that State” (paragraph 177). Third, “[a]ccordingly, the United Kingdom is under an obligation to bring an end to its administration of the Chagos Archipelago” (paragraph 178). Certainly, the Advisory Opinion was extremely adverse on the merits from a British perspective. However, the purpose of this piece is not to relitigate the merits of the case but, rather, to show that as a matter of procedure the opinion is not binding on the UK.

Critically, the ICJ considered the case under its “advisory” jurisdiction (Articles 65-68 ICJ Statute) rather than its “contentious” jurisdiction (Articles 34-36 ICJ Statute). Proceedings that occur under the auspices of the ICJ’s advisory jurisdiction do not have binding legal effect. If one is in doubt about this point, the ICJ’s own website sets out the position clearly. It states that “[c]ontrary to judgments … the Court’s advisory opinions are not binding. The requesting organ, agency or organization remains free to decide, as it sees fit, what effect to give to these opinions … [although] the Court’s advisory opinions nevertheless carry great legal weight and moral authority.” This merely reflects a long-standing acceptance that Advisory Opinions are non-binding that stretches back as far as the South West Africa Cases in 1962, where it was noted that “an advisory opinion…would not have binding force” and an adversely affected party “could continue to turn a deaf ear” to such a pronouncement. As Thin observes, “there is no legal basis upon which the ICJ AO would have [binding legal] effect… There is nothing in previous case law to indicate that ICJ AOs could have [binding legal] effect. There is nothing in the purpose behind ICJ AOs (to provide legal advice to international institutions, particularly the UNGA) to indicate that ICJ AOs could have this effect.”

To treat the ICJ’s Advisory Opinion as legally binding would be deeply problematic as it would set a precedent that allows the Court a route by which to circumvent the lack of State consent to its contentious jurisdiction. States are not bound by default to accept the contentious jurisdiction of the ICJ (for example, in territorial delimitation cases). Instead, they must actively consent to its contentious jurisdiction. There are several ways in which this can occur such as express agreement with the other State involved in the dispute, acceptance of jurisdiction in a treaty, issuing a declaration accepting jurisdiction and submission to the court. None of these applied in this particular case: the UK had strongly resisted the ICJ’s contentious jurisdiction and the general declaration that the UK has issued accepting ICJ jurisdiction in most matters specifically excludes “any dispute with the government of any other country which is or has been a Member of the Commonwealth” and this would include Mauritius. As the US Judge said in her dissenting opinion, this was a “quintessentially bilateral” contentious case and rendering an opinion “has the effect of circumventing the absence of United Kingdom consent.” To allow a “work-around” whereby the ICJ can simply pretend that what are really “contentious” cases are “advisory” requests and then, further, to claim that their decisions on those cases are binding, would represent a staggering enlargement of the ICJ’s competence that has no grounding in the UN Charter or the ICJ Statute. What should have happened here is that the ICJ should have acknowledged that this was a contentious case wearing an advisory mask. On that basis, it should have declined to render an opinion as it is entitled to do under (Article 65 ICJ Statute).

Dunne argues that there was no judicial overreach here as the ICJ was not “creating” law or passing a legal judgment per se but, rather, that the Advisory Opinion was “declaratory of the customary international law … of self-determination as it existed in 1965.” The effect of this position is that we should recognize the ICJ’s opinion as an authoritative statement of already binding law. However, that point does not stand up to scrutiny. As Milanovic notes, “when it comes to self-determination, the key question for the Court to decide was whether it was already a rule of customary law by 1968 [but] the Court completely fudges it. It simply relies on a series of GA resolutions, to which it expressly ascribes a normative character … and just asserts that self-determination was already customary at the relevant time. No state practice, no opinio juris, no nothing – just good plain assertion.” This confirms that what we see in this case is an unprecedented attempt by the ICJ to enlarge its competence by creating new law under the guise of its advisory jurisdiction. That effort should be resisted by States.

In short, the ICJ’s Advisory Opinion was non-binding. Regardless of its merits or lack therefore, it was not the product of a contentious process and therefore it did not have the capacity to impose obligations on the United Kingdom. Moreover, for the UK or any other State to treat the Opinion as if it did create such obligations, would be to give tacit approval to the Court to ignore the lack of State consent in future cases and to expand the jurisdiction of the ICJ far beyond what was intended.

United Nations General Assembly resolution (2019)

Three months after the release of the ICJ’s Advisory Opinion, the United Nations General Assembly passed Resolution 73/295 reaffirming the Court’s decision. It demanded that that all States respect the Chagossians’ right to self-determination (paragraph 2), that “the United Kingdom … withdraw its colonial administration from the Chagos Archipelago unconditionally within a period of no more than six months” and that the UK facilitates the resettlement of Mauritian nationals (paragraph 3).

Mauritius was unsurprisingly thrilled with this expression of support from the UNGA. Its legal team’s leader, Philippe Sands (a Briton, somewhat confusingly), commented that “I think this may be the first time in history that every African country has supported the resolutions at the General Assembly, the referral of the questions to the ICJ and then the subsequent question. There is absolute unity.” He went on to observe that “the UN and the ICJ had definitively resolved the dispute” and that “[v]ery frankly, what the United Kingdom wants in relation to the Chagos archipelago is, in a sense, neither here nor there.”

However, his confidence seems to be either feigned or misplaced. As noted above, the ICJ Advisory Opinion was non-binding (nor could it credibly be said to reflect existing customary international law). The UNGA resolution which builds on that Opinion is equally non-binding. As the UN Charter states, the General Assembly “may make recommendations” to States or to the Security Council but it does not have the capacity to make binding orders (Articles 10-17 UN Charter). This can be contrasted with the position of the Security Council whose decisions are legally binding, with Article 25 UN Charter explaining that members of the United Nations “agree to accept and carry out the decisions of the Security Council.” As the UN website itself summarizes, “resolutions adopted by the GA on agenda items are considered to be recommendations. They are not legally binding on the Member States. The only resolutions that have the potential to be legally binding are those adopted by the SC.”

In short, it is clear that UNGA assembly resolutions, including Resolution 73/295, are merely recommendations. Thus, Resolution 73/295 has no legally binding effect on the United Kingdom’s sovereignty over the Chagos Archipelago or its administration of the islands. Certainly, many countries have expressed displeasure with the UK’s position, however that is a political matter. Perhaps the countries that voted for the Resolution were unhappy with the UK based on other grievances. Perhaps they were keen to see a European power lose sovereign territory close to Africa. Perhaps lobbying from opposing powers such as Russia and China had encouraged States to lend their support to the Resolution. It matters little. Ultimately, as a matter of law, the UNGA resolution is a political utterance that represents a barometer of sentiment towards the UK. If a Resolution was passed tomorrow to recommend the stripping of overseas territories from France or Portugal, they would be similarly ineffective.

International Tribunal for the Law of the Sea judgment (2021)

The final pronouncement against the UK in the context of the Chagos Archipelago is from the International Tribunal for the Law of the Sea. Again, however, this decision has no binding legal effect compelling the UK to relinquish sovereignty of the Chagos Archipelago or affecting the delimitation of the UK’s territory. As will be explained in more detail below, this is because (i) the ITLOS Special Chamber assumed that the ICJ and UNGA pronouncements represented binding law when they did not and because (ii) on the basis of the first point, the UK was inappropriately excluded from the proceedings before ITLOS hence those proceedings cannot bind the UK.

On the first point, the ITLOS Special Chamber simply aligned with the prior statements of the UNGA and the ICJ in a manner that amounted to a disregard of its judicial responsibility. As Roeben and Jankovic note, the Special Chamber “did accept the GA determination as a given and, on that basis, proceeded to spell out an implication, ruling with constitutive effect on the aspect of sovereignty that is under its jurisdiction.” As noted above, UNGA resolutions have no binding legal effect, therefore to defer to them in this manner is inappropriate.

Regarding its reliance on the ICJ Advisory Opinion, the Special Chamber acknowledged that “it is generally recognized that advisory opinions of the ICJ cannot be considered legally binding”, but observed that “it is equally recognized that an advisory opinion entails an authoritative statement of international law on the questions with which deals” (paragraph 202). However, as noted above, this is incorrect as there was no clear customary international law position surrounding self-determination in the 1950s. The ICJ was simply concealing judicial law making behind a mask of judicial declaration of existing law. Separately, the Special Chamber stated that “judicial determinations made in advisory opinions carry no less weight and authority than those in judgments because they are made with the same rigour and scrutiny” (paragraph 203). This is also incorrect. There is a material difference between judgments and Advisory Opinions – if there was not then there would have been no need to furnish the ICJ with two separate jurisdictional capacities in the first place. As noted above, ICJ Advisory Opinions are not binding (and thus do not require State consent to jurisdiction) whereas ICJ judgments are biding (and thus do require State consent to jurisdiction). The fact that Advisory Opinions are made with the same “rigor and scrutiny” is irrelevant; otherwise we might get to the point where the ICJ bench could render a binding legal opinion by co-writing a monograph together. When it comes to law, forum and form matter.

On the second point, the result of the ITLOS Special Chamber’s deference to the UNGA and ICJ above was, as Thin notes, the “rather remarkable conclusion … that the dispute between the UK and Mauritius had in fact already been determinatively resolved … and that there was therefore no bar to jurisdiction.” Of course, this conclusion was wrong as the decisions were non-binding and so the UK remained sovereign over the Chagos Islands. However, the ITLOS Special Chamber’s error led it to decide that the UK was not an “indispensable” party to the present proceedings and that it could resolve a putative territorial dispute between Mauritius and the Maldives without allowing the UK to make representations. This was a violation of the principle established in the Monetary Gold that a court cannot exercise its jurisdiction over a question when a third state’s legal interests would “form the very subject-matter of the decision.” By definition, a UK legal interest (territorial sovereignty) was the subject matter of the present dispute between Mauritius and the Maldives and yet this was entirely ignored. The result was that, as Roeben and Jankovic summarize, the Special Chamber “found that it had jurisdiction to adjudicate upon the dispute between Mauritius and the Maldives [and] conclude[ed] that Mauritius can be regarded as the coastal State in respect of the Chagos Archipelago.”

What ought to have happened in the ITLOS proceedings was that the Special Chamber acknowledged that neither the ICJ Advisory Opinion nor the UN General Assembly Resolution resolved the Chagos Archipelago dispute. Thus, it should have declined jurisdiction in the absence of UK representation. Indeed, this was the view expressed in the dissenting opinion of Judge Oxman. Instead, the judgment was rendered and it prompted the UK Foreign Office to stress, correctly, that, “as not being a party to the proceedings, the UK is under no requirement to comply with the ruling.”

In short, the ITLOS decision to take jurisdiction over the putative territorial dispute between Mauritius and the Maldives was flawed because there was no extant binding international law or judgment that removed UK sovereignty over the Chagos Archipelago and thus the UK should have been a party to any proceedings concerning the sovereignty or territorial delimitation of those islands. In the absence of its participation, the UK cannot be said to be bound by the Special Chamber’s decision.

Conclusion

Sovereignty over the Chagos Archipelago has been the subject of a long dispute between the UK and Mauritius. A narrative is beginning to form that the combination of the ICJ advisory opinion, the UN General Assembly Resolution and the ITLOS Special Chamber decision furnish Mauritius with a solid claim to sovereignty over the island chain. This narrative is flawed. None of the decisions discussed above impose a binding legal obligation on the UK to vacate sovereignty: (i) the ICJ Advisory Opinion is “advisory” only; (ii) the UN General Assembly resolution is a “recommendation” and (iii) the ITLOS proceedings did not involve the UK and therefore do not have the capacity to bind the UK. For the UK to relinquish sovereignty based on a false narrative that lacks the foundation of an enforceable legal judgment would be an error.