Invoked as moral authority, the International Court of Justice‘s reasoning collapses under its own logic, elevating consent in theory while sidestepping it in practice.
In 2019, the International Court of Justice issued an advisory opinion declaring that the UK had unlawfully separated the Chagos Archipelago prior to independence and should bring its administration to an end “as rapidly as possible”. Despite being non-binding, this opinion is now routinely presented as if it settles the matter entirely.
Indeed, the first defence you now hear, almost by reflex, from Labour MPs when discussing Keir Starmer’s Chagos deal is this: the International Court of Justice has spoken. Case closed.
But the more closely one reads that advisory opinion, the harder it is to escape a series of profound contradictions at its core.
The International Court of Justice, an advisory court of just 15 judges drawn from around the world, including Russia and China, presented its reasoning as a defence of self-determination. Yet in doing so, it appears to have undermined the very principle it claimed to uphold.
The Court’s argument rests on a simple and powerful idea, that the detachment of the Chagos Archipelago from Mauritius in 1965 was unlawful because it denied a people their right to self-determination. Consent, freely and genuinely expressed, is elevated to the status of a foundational legal requirement. Without it, sovereignty is tainted.
So far, so compelling.
And yet, having established consent as the decisive test, the Court declines to apply that same test where it matters most, in the present. In 2026. Now. Today.
Instead, the will that counts is the will of a colonial unit as it existed in the 1960s. The will that does not decisively count is that of the Chagossians themselves, the very people whose lives, identity, and future are directly bound up in the fate of the islands.
This is not a technical nuance. It is the central flaw.
If it was unlawful in 1965 to alter sovereignty without “the free and genuine expression of the will of the people”, then on what principled basis can it now be considered lawful, or even acceptable, to contemplate a transfer of sovereignty without clearly establishing the freely expressed wishes of the Chagossians today?
A principle that is applied rigorously to the past, but selectively to the present, ceases to be a principle at all.
But the tension does not end there.
The opinion insists, formally, that it is merely advisory, not binding, not enforceable. And yet its language is anything but tentative. The United Kingdom is told it must bring its administration to an end “as rapidly as possible”, while other states are called upon to support that outcome. This is advice framed as instruction, authority asserted without the discipline of enforceability.
There is also a deeper structural inconsistency. The Court speaks the language of people, of rights, of self-determination. But the mechanism it applies is territorial. What ultimately matters is not the clearly expressed will of a living community, but the preservation of the boundaries of a colonial administrative unit as it existed decades ago. A principle rooted in human agency produces an outcome governed by cartography.
Even the most morally compelling element of the case, the forced displacement of the Chagossians, is handled in a way that exposes this imbalance. The Court acknowledges it, invokes it, draws moral force from it. Yet when it comes to legal consequence, it is set aside, treated as a separate human rights issue to be addressed elsewhere, perhaps by the United Nations General Assembly. The people at the heart of the injustice are, once again, not at the centre of the decision.
The Court further characterises the situation as a “continuing wrongful act”, effectively freezing the legal analysis in time, as though the decades since 1965, the displacement of an entire population, and the complex realities of governance, security, and international relations had not intervened. Law is applied as if history has stood still.
And throughout, there is a striking imbalance between reach and restraint. The Court reaches sweeping conclusions about legality and obligation, yet declines to engage with the real-world consequences of those conclusions, security, environmental stewardship, governance, compensation. It is maximalist in principle, minimalist in responsibility.
What emerges is an uncomfortable picture. The Court condemns the absence of consent in a historical moment, yet appears willing to tolerate, or at least sidestep, the absence of consent in the present. It elevates self-determination in theory, while constraining it in practice. It privileges the territorial integrity of a long-defunct constitutional arrangement over the agency of a living, displaced community.
This is not consistency. It is contradiction.
And it matters, because this advisory opinion is now being wielded as a decisive moral and legal justification in contemporary policy. It is treated not as one legal view among many, but as a kind of final authority. Yet it is neither binding, nor beyond challenge. It is the product of 15 judges, not an infallible pronouncement, and its reasoning must stand or fall on its coherence.
On that test, it struggles.
The bottom line is this. It is 2026. If self-determination is the guiding principle, then it must apply to the people who exist today, not only to a constitutional snapshot from the 1960s. The Chagossians must have a decisive voice in determining their future, not a peripheral one, not a deferred one, but a central and determinative one.
Otherwise, what is presented as a defence of self-determination begins to look, uncomfortably, like its opposite, a doctrine invoked to correct the past, but incapable of guiding the present.
Don’t take my word for it, read the ICJ’s advisory opinion yourself and see the contradictions: https://www.icj-cij.org/node/105778
By Claire Bullivant, CEO Great British PAC
