The Evolution of the Chagos Islands Sovereignty Dispute
The Chagos Islands have been at the centre of a long-running sovereignty saga between the United Kingdom and Mauritius for over fifty years. For decades, the two have been intractable: the UK government had repeatedly insisted that Mauritius itself had no legitimate claim to the Islands while Mauritius consistently criticises the last vestiges of British colonialism on its doorstep. However, on 3 October 2024, the UK announced that it was conceding its claim to sovereignty over the archipelago to Mauritius in a historic move. Despite this, the prospect of finalising a deal has been stuck in limbo in recent months, riddled with several recent complications. The evolution of the sovereignty dispute and how progress on the recent agreement has faltered merits closer inspection.
The Chagos Islands are host to a vivid history. Though cited by Sultan Hassan IX as an extension of Maldivian maritime territory in 1560, the Islands were largely inhabited until catching the Portuguese’s attention in the late sixteenth century. Situated on international trade routes, the Islands quickly became chess pieces in the historic European rivalries that dominated the early modern period. In 1786, France took possession of the Chagos Archipelago and Seychelles as dependencies of Mauritius. Slaves were imported from Africa during this period, resulting in the development of a plantation economy. The Napoleonic Wars witnessed Britain seize Mauritius and its dependences – including the Islands – from France, later proclaimed a colony of Britain in 1814 under the Treaty of Paris.
After the chopping and changing of hands, the Islands remained firmly under British control and were governed from Mauritius. As Mauritius was poised for independence in 1968, the UK controversially split the Chagos Archipelago away from Mauritius on 8 November 1965 with the agreement of the Mauritian government to formally establish the British Indian Ocean Territory (BIOT). This was followed by a nebulous chapter in postwar colonialism under Harold Wilson’s tenure, whereby the UK removed the local population of approximately 1,700 Chaggosians – of mixed African, Indian, and Malay descent – between 1968 and 1973, to pave the way for a strategic joint UK-US military base on Diego Garcia which remains in operation today. Many Chaggosians were then resettled to Mauritius, the Seychelles, and later the UK whilst several laws made by the UK’s Commissioner made it illegal to return or stay without permission.
The agreement reached on 3 October 2024 represented uncharted territory in the dispute’s history. Under the terms of the proposed UK-Mauritius treaty, the UK and Mauritius agreed that Mauritius is sovereign over the Archipelago, including the strategic Diego Garcia military base. Accordingly, the UK agreed, for a 99-year initial period to lease the base and exercise “the sovereign rights and authorities of Mauritius required to ensure the continued operation of the [Diego Garcia military] base well into the next century”. Furthermore, the agreement includes provisions for greater cooperation on environmental protection, combating illegal fishing, a new Mauritian Marine Protected Area (MPA), UK funding to Mauritius to “enable” a new “economic, security and environmental partnership”, and a resettlement and visitation programme for Chaggosians. This represented a sea change in the UK government’s attitude, and it is worth deciphering why policy has shifted in recent years from its previous unyielding stance.
The erosion of the UK’s legal position as the United Nations’ (UN) top courts and general assembly has been one factor. A pivotal blow arrived when Mauritius challenged the UK’s decision to establish a MPA around the Islands in 2010 as an infringement of sovereignty, and the Permanent Court of Arbitration (PCA) ruled that the UK’s creation of the MPA violated the UN Convention of the Law of the Sea (UNCLOS) in 2015. Later judgements swiftly followed such as when the UN General Assembly requested the International Court of Justice (ICJ) to issue an advisory opinion on the Chagos dispute in 2017, resulting in the 2019 ruling that the UK's continued administration is unlawful and that the islands should be returned “as rapidly as possible”, subsequently approved by the UN General Assembly in a 116-6 resolution in favour of calling for the UK to end its administration of Chagos within six months. A dramatic coda arrived when the International Tribunal for the Law of the Sea (ITLOS) ruled in favor of Mauritius' sovereignty over Chagos in 2021.
Secondly, African nations have spoken recently with greater unanimity, condemning what many consider to be the UK’s “last African colony”. The African Union (AU), fervent in its efforts “to ensure the decolonization of the Chagos Archipelago”, participated in public hearings before the ICJ on the 3 September 2018 on the request for an advisory opinion regarding the Islands’ separation from Mauritius (a Member of the AU) in 1965. Arguably, the AU have taken proactive strides on their own – in the AU’s Assembly decision on the UN General Assembly vote in February 2019, it urged Member States to “redouble their efforts” and “remain actively seized in the matter”. This was evident following the UN deadline for the UK to relinquish control over the Chagos Islands expired on November 22 2023 and the AU Commission chairperson, Moussa Faki Mahamat, was quick to reiterate calls for the UK to complete its decolonisation in line with the AU’s Constitutive Act.
Finally, Mauritius herself has waged an increasingly sophisticated campaign via global forums, the highest courts, and the media. It was the Mauritian government who initiated proceedings against the UK in the case before the PCA in 2010 and in the Case before ITLOS against the Maldives in 2021 regarding the boundaries of their respective Exclusive Economic Zones (EEZs) which reiterated the ICJ’s condemnatory ruling regarding the UK’s sovereignty over the Chagos Islands themselves. Likewise, the Mauritian government leveraged the power of the media when the Mauritian flag was raised on the British-controlled islands for the first time in 2022. The government-sponsored media spectacle drew together a litany of theatrical elements to hammer home a clear message. Led by the Mauritian ambassador to the UN on the atoll of Peros Bahos, the Mauritian flag was raised whilst an emotional pre-recorded message played from then Prime Minister Pravind Jugnauth, unequivocally proclaiming Mauritius as “the state with sovereignty”.
The effect of the geopolitical tide against the status quo was evident when on 3 November 2022, then British Foreign Secretary James Cleverly announced that the UK and Mauritius had decided to begin “negotiations on the exercise of sovereignty” . Balancing recent international proceedings levelled against the UK with the UK's own attempts to uphold international law in response to the Russian 2022 invasion of Ukraine had perhaps become untenable. Additionally, Britain’s resistance to the handover was derailing the UK’s ability to build relations in Indo-Pacific likely conflicted with the objective of wooing post-Brexit trading partners. Cleverly’s statement certainly represented a far cry from the uncompromising rhetoric of Sir Alan Duncan, then Minister of State for Europe and the Americas under Thersea May, who stated in 2019 that “Mauritius has never held sovereignty over the Archipelago and we do not recognise that claim.”
Progress under successive Conservative governments was slow. Though negotiations began under Liz Truss’ brief stint as UK Prime Minister, talks appeared tepid on the UK’s part. Though Rishi Sunak agreed to open talks once more in November 2022, scarce media attention revealed little about the progress made by these stages. Sight of an agreement was perhaps damaged by former British prime minister Boris Johnson’s scathing criticism of a deal as a “colossal mistake” in September 2023, followed by the publication of a paper by the influential right-wing thinktank Policy Exchange opposing the transfer as a “major self-inflicted blow”. Rather interestingly, questions of responsibility have developed into a spat amongst two former Tory prime ministers, with Truss and Johnson recently trading barbs in a blame game over Starmer’s recent agreement.
It was Labour’s election victory in July and Sir Keir Starmer accession as prime minister which hastened negotiations on the agreement table by October 2024. The joint-statement released by Sir Keir and Mauritius Prime Minister Pravid Jugnauth is revealing of how Starmer’s values and foreign policy outlook intersect: “this is a seminal moment in our relationship and a demonstration of our enduring commitment to the peaceful resolution of disputes and the rule of law.” Though the UK is relinquishing territorial control of the Islands, Starmer is content to emphasise that it is being achieved both peacefully and legally. As a former human rights barrister and Director of Public Prosecutions (DPP), it comes as little surprise that his motivations align with a desire to strictly observe the rule of international law and, in his eyes, an arrangement by which Britain cedes sovereignty but then leases back its base on Diego Garcia is a means for the government to abide by international law while continuing to support defence interests.
That said, the “seminal moment” has since fallen victim to the twists of international fate because of two recent elections. The deal had been finalised shortly before then-Prime Minister Pravind Jugnauth’s was defeated in a landslide on 10 November 2024. His successor, Navin Ramgoolam, concluded to the Mauritian Parliament in December that the deal was unpalatable and “would not produce the benefits that the nation could expect from such an agreement”, before sending revised proposals to the UK government on 17 December. Shortly after, Deputy Prime Minister Paul Bérenger hinted that the decisions were slowing down over finances, complaining that "[UK negotiators] are trying to make us sign and they are quibbling on a small amount”, and stressing to the Mauritian Parliament the need for greater financial contributions to alleviate Mauritius’ economic woes.
Donald Trump's re-election as president in November 2024 has had a profound impact on the progress of the agreement. Initially, the UK government aimed to finalise a deal before Trump's inauguration on January 20, 2025. However, a Mauritian source told the BBC that “overnight the British position changed.” Following this, on January 15, 2025, a spokesman for Starmer stated that the incoming Trump administration would be consulted to “consider” the deal – a clear indication that the UK is seeking White House’s blessing. While President Trump has yet to publicly comment on the agreement, his administration was expected to take a more critical stance than his predecessor, explaining the UK government’s apprehension. In contrast, President Biden had praised the “historic agreement”, emphasising its role in securing the future of a base crucial to national, regional, and global security. However, Trump’s inner circle has expressed ire – if not outright opposition – to the deal.
Secretary of State Marco Rubio previously warned in an interview with POLITICO that the agreement poses a “serious threat” to U.S. national security and “critical U.S. military posture.” Similarly, Robert Wilkie, who led Trump’s Department of Defense transition team, described it as a “calamitous decision” that fails to account for long-term security implications. These concerns resonate with Republicans who fear that Iranian university branches in Mauritius could facilitate espionage on Diego Garcia should the UK relinquish control of the island. Additionally, top Republicans have urged Trump to veto the deal, arguing that it could enable greater Chinese commercial influence in the Chagos Islands - potentially leading to Chinese surveillance of the U.S. base or even the establishment of a Chinese military presence in the region.
China’s longstanding ties with Mauritius further fuel these concerns. The i newspaper reported that China has also supported the development of Mauritius’ state broadcaster headquarters, a dam, and a sports complex. Moreover, Mauritius was the first African nation to sign and implement a free trade agreement with China. This is expressive of the Trumpian focus on countering Chinese influence – thematic of recent discussions regarding the annexation of Greenland and retaking control of the Panama Canal. The UK government has responded to its counterpart’s concerns, demonstrated by its emphasis on safeguarding against China’s “malign influence.” Starmer used this phrase with his Mauritian counterpart, Navin Ramgoolam, in their January 31 discussion – an expression that Marco Rubio also echoed in a recent conversation with UK Foreign Secretary David Lammy. As Lammy prepares to meet with Rubio in the coming weeks, this theme will likely dominate their discussions as he seeks to persuade his US counterpart that the agreement remains a “good deal”.
Beyond Trump, securing the agreement will also require Sir Keir to navigate domestic opposition. Criticism from the right, particularly within the Conservative Party and right-wing circles, has been prominent. Trump ally and Reform leader Nigel Farage has warned that the deal could dangerously fracture the UK-U.S. relationship, stipulating that if the UK ceded sovereignty to Mauritius, the UK’s “value” in the “special relationship” would become “considerably reduced”. Meanwhile, Conservative leader Kemi Badenoch has raised concerns about the financial implications of the agreement, suggesting hidden costs that could burden the UK by up to £18bn and calling it an “immoral surrender” - claims that Labour denies. Opposition remains strong among those who see the deal as an expensive concession rather than a strategic necessity.
Beyond financial and geopolitical concerns, the agreement also raises questions about the broader implications for other UK overseas territories. The agreement could set a precedent for similar arrangements elsewhere, particularly in Cyprus – where Britain maintains two sovereign military bases (Akrotiri and Dhekelia) – and the Falklands Islands, where Argentine claims to sovereignty remain contentious.
Then there is the question of the Chagossians themselves. While the deal is framed as a step toward justice for the islanders who were forcibly removed from their homeland in the 1960s and 1970s, many Chagossians feel sidelined in the negotiations. There is no single, unified Chagossian position, with some advocating for full sovereignty under Mauritius and others preferring continued UK governance. The lack of direct consultation has fueled criticism and, arguably, the Chagossians’ voices have been drowned out by the broader geopolitical concerns outlined.
At present, the deal appears to be satisfying no one entirely. The Trump administration is sceptical, Conservatives are damning, Chagossians feel unheard, and Mauritius remains difficult. And yet, despite the mounting opposition, the agreement may still manage to pass – if only as a pragmatic compromise rather than a triumph of diplomacy. As the White House continues to review whether to endorse or scupper the deal, Starmer’s government will need to thread the needle between appeasing Washington and defending the deal against domestic critics. Whether the agreement ultimately survives or rolls back under pressure remains to be seen.
Image courtesy of NASA via Earth From Space, ©1990. Some rights reserved.
The views and opinions expressed in this article are those of the author and do not necessarily reflect those of the wider St. Andrews Foreign Affairs Review team.
