Did the UK act illegally in splitting off the Chagos Islands from Mauritius prior to its independence in 1968? Mauritius successfully petitioned the UN to ask the International Court of Justice (ICJ) to consider this question, against the UK's wishes, but the outcome might not be what either country is hoping for.

Following a vote in the UN last June, the ICJ is due to consider the "legal consequences" of the separation of the Chagos Islands from Mauritius in 1965, three years before Mauritius gained independence. The deadline for written submissions has been extended to March 1, 2018. It's probably fairly easy to guess what the Mauritian and UK government submissions will contain. But there are more players involved than just those two countries. Most importantly, there are the Chagossians themselves, who were forcibly exiled from the archipelago to make way for what is now a full-fledged US military base on the island of Diego Garcia.

The UK maintains that the Chagos Islands were only administered by Mauritius "as a matter of convenience" (PDF) and were not really a part of Mauritius' territory. It will also point to the agreement it signed with the Mauritian colonial administration in 1965, under which the UK paid Mauritius 3 million British pounds ($4.2m) in recognition of the detachment of the Chagos Islands and gave undertakings to cede the islands to Mauritius when "no longer needed for defence purposes" as well as other benefits including fishing and mineral rights.

Mauritius will argue the opposite: that the Chagos Islands are an integral part of Mauritius and the agreement with the UK was "obtained under conditions of duress and coercion" (PDF).

Far from having to hand sovereignty to Mauritius, the UK may find themselves under an international legal obligation to ensure the Chagossians are able to exercise their right to self-determination, which will mean facilitating their plans to return to their Indian Ocean home.

But the wording of the UN resolution that the Court will address is fairly broad, allowing the ICJ to look beyond the core question of sovereignty, to consider wider issues of decolonisation and the exercise of the right to self-determination.

This means the Court can look, for example, at whether the UK breached some of its obligations towards the former inhabitants of the Islands. Over the years, the UK has taken exceptional steps to prevent the Chagossians from returning to the Islands; a sign, maybe, of its own uncertainty over the legality of its actions. In 2000, it withdrew the Chagossian right of abode in the British Indian Ocean Territory (BIOT) - as the UK calls the Chagos Islands - and, in 2004, it reinstated full immigration restrictions over the BIOT. In 2010, it declared a controversial marine protected area around the BIOT which was later rendered unlawful by an international tribunal. And it is worth remembering that it was against the background of the UN-inspired decolonisation process in the 1960s, that the US and UK governments covertly agreed that the entire population of the Chagos Islands would be removed before the US government took possession of Diego Garcia.

Despite knowing that the Chagos Islands supported an indigenous population which was ethnically and culturally distinct, the UK government chose not to disclose this information to the UN General Assembly, possibly for fear that the BIOT would be classified as a non-self-governing territory. Under Chapter XI of the UN Charter, countries which administer "territories whose peoples have not yet attained a measure of self-government" have to ensure and promote the interests and the well-being of the inhabitants of these territories and to transmit relevant reports to the UN Secretary-General. If the BIOT were deemed a non-self-governing territory, it would mean the Chagos Islanders had the right to choose their own political future and achieve self-government. It would also mean that the UK, as the "administering State", did not have the right to divide up or dismember the BIOT in violation of self-determination, as leading expert, Stephen Allen, argues. Or, indeed, forcibly remove the inhabitants and prevent their return.

So, despite what Mauritius is hoping for and what the UK fears, the Court's advisory opinion might not hinge on UK sovereignty of the Chagos Islands, but on their status. Far from having to hand sovereignty to Mauritius, the UK may find themselves under an international legal obligation to ensure the Chagossians are able to exercise their right to self-determination, which will mean facilitating their plans to return to their Indian Ocean home. Not the outcome that Mauritius or the UK - or the US - are hoping for, but one that would be welcomed by those Chagossians who have been campaigning for the right to return for over 40 years.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial stance.