After several years of stop-start negotiations involving both Conservative and Labour governments in the UK, compounded by uncertainty following Donald Trump’s election as US President, and a last-minute legal challenge, an agreement was signed on 22 May 2025 to cede—or return—sovereignty of the Chagos Archipelago to Mauritius. In turn, Mauritius agreed to grant the UK and US continued, unrestricted military access to Diego Garcia. While the agreement is not without its critics, particularly among right-wing politicians, commentators, and media, it represents a significant achievement for diplomacy, the rule of law, and the broad-er process of decolonisation.
Formally titled CS Mauritius No.1/2025, the agreement sets out a 99-year framework—extendable by a further 40 years, with the UK committing to pay Mauritius about £101 million annually (at present prices). With UK recognition of Mauritian sovereignty, Mauritius has granted the UK and US the right to maintain and operate the existing military base, conduct exercises, and carry out defence and security operations. The agreement also provides for unrestricted over-flight rights, allowing UK and US military aircraft to cross the archipelago without prior notification, and grants full navigation and undersea transit rights to vessels and submarines from both countries.
The agreement also includes safeguards to prevent hostile actors from gaining a foothold in the region. A 24-nautical-mile buffer zone will be established around the island, within which no construction or installations can take place without the UK’s approval. In addition, any activity on the wider Chagos islands must go through a joint decision-making process, meaning no development can proceed without the agreement of both the UK and Mauritius. There is also a ban on the presence of foreign security forces, whether military or civilian, on the outer islands.
Beyond the military aspects of the agreement, the treaty allows Mauritius to implement a resettlement programme on islands other than Diego Garcia, subject to environmental and security conditions. It also commits both parties to preserving the archipelago’s marine biodiversity, via the existing Marine Protected Area. In addition, the agreement includes provisions to support the Chagossian community—estimated at over 3,000 people—through resettlement assistance and cultural initiatives. The UK will contribute £40 million to a Chagossian trust fund and provide £45 million annually for 25 years to support development projects in Mauritius. Overall, the agreement is framed as a full and final settlement of all disputes, with mechanisms for peaceful resolution and long-term bilateral cooperation.
On announcing the agreement, the Labour Government reiterated its long-held position that there was no alternative. A press release stated, “Without this deal, international legal proceedings could have rendered the base inoperable”. The government was especially concerned about the 2021 ruling by the Special Chamber of the International Tribunal for the Law of the Sea and a likely follow-up judgement, which would have damaged the UK’s ability to operate in and around the archipelago. The government argued that Diego Garcia’s satellite communications might be compromised, as the UK relies on UN authority to access a specific segment of the electromagnetic spectrum. It also claimed that contractors might refuse to travel to the base—for maintenance or supplies—due to fears of legal action from Mauritius. Additionally, the UK’s ability to operate aircraft to and from the island could face challenges under international aviation rules. Without an agreement, there were also fears that it would be easier for foreign powers to establish a presence in the islands.
The reaction to the agreement was unsurprisingly mixed, but crucially members of the Trump administration were supportive. Secretary of State Marco Rubio said, “following a comprehensive … review, the Trump Administration determined that this agreement secures the long-term, stable, and effective operation of the joint US-UK military facility at Diego Garcia”, while Defense Secretary Pete Hegseth noted, “The UK’s deal with Mauritius secures the operational capabilities of the base and key US national security interests in the region. We are confident the base is protected for many years ahead”. The UK Government denied the US could have vetoed the deal, but without such support, the agreement would have been more difficult to secure and de-fend.
The position of the Trump administration meant that right-wing opponents to the deal in the UK were rather hoist by their own petard, as they had claimed that the US would ultimately speak out against the deal. Nevertheless, in the House of Commons debate that followed the signing of the treaty and in the resulting press coverage, the language was sharply against. For example, the Shadow Defence Minister, James Cartlidge, argued that the agreement was “a total, abject surrender of our territory and a fundamental betrayal of the UK’s national interest” and “a complete and utter negotiating failure”. And Richard Tice of Reform stated, it was “the worst ever deal in history by this country”. These sentiments were mirrored in parts of the press. For instance, The Times, on its leading articles page, called the agreement “a lawyers’ stich up, a shameful sell-out”, while an editorial in The Daily Telegraph declared, “Starmer’s Chagos surrender is a national disgrace”. It is certainly true that parts of the agreement are stronger than others and there is a crystal ball element to how some of the practicalities will work out longer-term, but the language used by many on the right has not done justice to this nuanced issue.
There are a few more measured critical voices, such as John Rentoul in the Independent, but he downplays Mauritius’ legitimate and increasingly supported territorial claim. And this is the key issue—the process of decolonisation needed to be completed as I detailed in a previous article. As Navin Ramgoolam, prime minister of Mauritius said, “We have gained recognition of our sovereignty over the entire archipelago of Chagos, including Diego Garcia, which completes the process of decolonisation which began in 1968”. Notwithstanding, important and sustained support is required for the Chagossians both in the UK and Mauritius, including through the possibility of re-settlement, but despite how unfair it might seem any deal had to be made between the sovereign states. Yet, some Chagossians are supporting it—Olivier Bancoult, leader of the Chagos Refugees Group, said it was “an historic day”, and that “[our children] will finally be able to walk the land of their ancestors”.
For many years, the Chagos Archipelago, also known as the British Indian Ocean Territory (BIOT), has been one of 14 British Overseas Territories (OTs). However, for the first time since Hong Kong was returned to China in 1997, that number will be reduced to 13—a significant change. As I have argued previously, however, the transfer of sovereignty over Chagos is unlikely to trigger the loss of other OTs, unless their populations actively seek such a change. And to reinforce that message, the Falkland Islands, released a public statement noting that “Our situation is unique to the Falklands and is entirely separate to the sovereignty of the Chagos Islands”.
Although the agreement has not yet been approved by Parliament, the most challenging aspects of the negotiations have been completed. It addresses a longstanding issue that has affected the UK’s international reputation; it contributes—though not fully—to strengthening the position of the Chagossians in the UK, Mauritius, and the archipelago; it secures a strategically important military asset; and it shows that a solid diplomatic argument can gain traction in the Trump White House. However, much of the political and media commentary on the issue has been reductive and dispiriting and illustrates the increasingly polarised and detrimental nature of public discourse in the UK.
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