The British Indian Ocean Territory: Clouds on the Horizon for Diego Garcia? – Dr Peter Harris

18 August 2020 Leighton G. Luke, Research Manager, Indo-Pacific Research Programme Download PDF

Key Points

  • The strategically located British Indian Ocean Territory was created in 1965, when the islands (also known as the Chagos Archipelago), were excised by London from Mauritius for defence purposes and their residents deported. The island of Diego Garcia is home to the US Naval Support Facility.
  • UK sovereignty over the islands has been ruled to be illegitimate in the 2019 Advisory Opinion of the International Court of Justice and by the United Nations General Assembly.
  • US and British concerns over Mauritian sovereignty are largely centred on the possibility that Mauritius might someday decide to evict the US military from Diego Garcia.
  • For Mauritius, retaining the US presence is of strategic and financial value and Port Louis has stated its willingness to offer Washington a 99-year lease over Diego Garcia. For the US, reaching a lease agreement with Mauritius would remove all legal and moral questions about the use of Diego Garcia as a base.
  • Mauritius, the UK and the US all belong on the side of democracy, decolonisation, and a rules-based international order in the Indo-Pacific. In the end, all will agree that decolonisation of the Chagos is not just the ethical choice, but also the strategic course of action.


In view of the growing interest in the circumstances surrounding the sovereignty of the British Indian Ocean Territory (also known as the Chagos Archipelago), which is home to the highly strategic US Naval Support Facility Diego Garcia, FDI is very pleased to discuss these matters with Dr Peter Harris, assistant professor of political science at Colorado State University and an expert on the situation in the Chagos Archipelago.


The British Indian Ocean Territory (BIOT) enjoys a highly strategic location in the centre of the Indian Ocean, about 1,770 kilometres east of the Seychelles and 2,180km north-east of Port Louis, Mauritius. The territory, an archipelago of 58 islands also known as the Chagos Archipelago, covers some 640,000km2 of ocean. The islands have a total land area of only 60km2. Diego Garcia, the largest and most southerly island, has an area of 44km2. The terrain is flat and low and most areas do not exceed two metres in elevation.

Administratively, BIOT was formed in 1965, prior to Mauritian independence three years later, with the detachment of the islands from Mauritius and the payment by London to Port Louis of a £3 million compensatory grant. BIOT is administered from London, by a Commissioner appointed by the Queen. In the Territory itself, the civilian administration is represented by a Royal Navy Commander, who is appointed as the Commissioner’s Representative. As well as being the highest civilian authority in the Territory, this person is also the Officer commanding the British Forces in Diego Garcia. The post is currently held by Commander Kay Burbidge. London has maintained that it will eventually turn the archipelago over to Mauritius when it is ‘no longer needed for defence purposes’.

Between 1,400 and 1,700 residents of the archipelago, known as Chagossians or Ilois, were relocated by the British authorities to Mauritius and the Seychelles in the 1960s and 1970s. In 1971, Diego Garcia was closed when the island was deemed necessary for defence purposes under the 1966 UK-US Exchange of Notes. Diego Garcia is home to approximately 3,000 UK and US military personnel and civilian contractors.[1]


FDI: Thanks for your time today, Peter. What factors would have to come into play to bring about a change in the sovereignty of the British Indian Ocean Territory (BIOT), or Chagos Archipelago?

PH: For any part of the Chagos Archipelago to come under Mauritian sovereignty, the UK Government would have to agree to a transfer. At the moment, London is set against the idea. But there are a few ways to imagine this changing. First, the UK Government could come to believe that it is more important to uphold the international law on decolonisation (as described in the International Court of Justice advisory opinion and successive UN General Assembly resolutions) than to uphold its (arguably illegal) executive agreement with the US. This is unlikely to happen under the Conservatives, who prize the so-called “special relationship” with the US, but it could feasibly happen if the Labour Party wins a general election. It almost certainly would have happened if Jeremy Corbyn had become Prime Minister. Second, the UK could be persuaded to relinquish Chagos if the US decided that it preferred Mauritius as a landlord over the UK. Again, this seems like an unlikely outcome at the moment but it is not unthinkable: there are strong reasons to believe that UK sovereignty is becoming more trouble than it is worth from the US perspective, and that Washington might soon come to prefer an arrangement with Mauritius that would remove all legal and moral questions about using Diego Garcia as a base. If the US asked the UK to step aside and allow decolonisation to proceed, there would be no reason for the UK to deny this request.

FDI: For Mauritius, what is the motivation for, and benefits of, acquiring sovereignty over BIOT? 

PH: Sovereignty over the Chagos Archipelago has been a hot-button issue in Mauritian politics since the 1980s. The territorial claim is enshrined in the Constitution. Left-wing groups such as Lalit have grasped onto the issue, but so have the mainstream political parties. In other words, this is not a territorial claim that Mauritian leaders can simply give up; they would face a severe backlash if they tried. Rather, Mauritian leaders face compelling incentives to be seen as fighting to regain Chagos. This domestic climate means that any sitting Mauritian Prime Minister would seek sovereignty over Chagos even if there was no material benefit from controlling the islands. It is just something that Mauritian governments are hardwired to do.

Of course, it does not hurt that regaining control of Chagos would, in fact, bring several material benefits to Mauritius. First, the territorial size of Mauritius would increase dramatically (by over 245,000 square miles) if Port Louis took control of the Chagos Islands and surrounding exclusive economic zone. Second, whoever controls Chagos is also the owner of the Great Chagos Bank, the largest coral reef structure in the world (much of it in pristine condition), which presents opportunities in terms of conservation and building a “green legacy.” Third, there would be an opportunity for Mauritius to charge the US rent for the use of Diego Garcia – potentially a large annual sum. Fourth, hosting a US base would expand and cement the US-Mauritian defence relationship, creating a reliable expectation that the US would come to Mauritius’s aid if ever its security came under threat by a hostile power. This would be doubly beneficial for Mauritius because it would allow Port Louis to avoid over-reliance on India as a security-provider; two great-power patrons are better than one. Finally, there is dignity in insisting that decolonisation be completed. This final point should not be underestimated: Mauritians want their territory to be returned to them simply because it belongs to them, and because it is an unconscionable affront for the UK to insist on retaining sovereign control despite the overwhelming international consensus that Britain’s occupation of Chagos is illegal.

FDI: What is it exactly that the UK and the US see themselves as standing to lose if the sovereignty of BIOT were transferred to Mauritius?

PH: This is a great question and it has never been answered candidly by UK or US officials in a public forum, as far as I can tell. I can think of a few fears that might motivate the British and Americans, but I would love to see any of my conjectures confirmed or denied by an official spokesperson. First, there is the question of whether Mauritius would allow the US to use Diego Garcia as a military base in perpetuity. Port Louis says that it will agree to a 99-year lease over the island, but is that credible? The whole point of keeping the Chagos Islands under British sovereignty in 1965 was so that the US would not have to deal with a postcolonial African state. To be blunt, the US still does not want to deal with such a state. The Americans would prefer deal with their British counterparts, whom they trust more than the Mauritians. My own view is that there is a racist and imperial mindset at play here: Mauritius is being judged as unfit to govern its own territory. Second, the US would presumably prefer to avoid paying rent to Mauritius, given that it does not pay the UK an annual sum right now. Third, Mauritius might impose restrictions on the usage of Diego Garcia that would be more stringent than any limitations required by the British. After all, BIOT is a territorial jurisdiction that exists solely for the benefit of Naval Support Facility Diego Garcia. Once the islands become “just another” part of Mauritius, they will be made subject to all kinds of laws that do not exist on the books in BIOT – laws to do with human rights or arms control, for example. This might be inconvenient for the Pentagon. Finally, Mauritius would allow the resettlement of some or all of the Chagos Islands by the indigenous Chagossians (and perhaps other Mauritians), which Britain has always opposed. The fear is that a permanent civilian population anywhere in Chagos would compromise the operability of the base on Diego Garcia.

FDI: What is the likelihood of Mauritius later deciding to order the closure of the US military facility on Diego Garcia?  

PH: It is always a possibility that a sovereign nation decides to eject foreign troops from its soil. That is an unavoidable condition of hosting troops overseas, and it should not be regarded as unfair or suspect – and still less unique to this situation. The Filipino Government closed the US base at Subic Bay in the 1990s, for example, and the US presence in Okinawa is deeply controversial. But my view is that Mauritius is unlikely to close the base – especially if the US can secure a binding legal agreement. There are several benefits that Mauritius would get from hosting a US base: not just rent, but also an implicit security guarantee from the world’s most powerful military. Moreover, it must be remembered that the current arrangement with the UK is not enforceable; there is absolutely nothing to stop Britain deciding to abrogate the current UK-US executive agreement (which gives the US access to Diego Garcia) on the basis that the decolonisation of Chagos is a higher obligation under international law. Only Mauritius is in a position to offer the US a binding agreement to govern access to Diego Garcia. From this view, paying rent to Mauritius for the use of Diego Garcia would be a good problem to have: it would mean that the US had secured an above-board legal agreement to secure the future of its base.

FDI: A major regional actor is India. What, if any, outlook or policies with regard to a continued US presence on Diego Garcia would India seek to develop, particularly in view of the India-China situation?

PH: India is sometimes mentioned as a threat to the US presence on Diego Garcia. The argument is that India has long regarded itself as a “big brother” to Mauritius; a security-provider and guarantor of sovereignty. As such, India might oppose a continued US military presence on Diego Garcia once it is returned to Mauritian sovereignty. India might even want Diego Garcia for itself. But those fears are misplaced. India’s biggest security challenges come from Pakistan (on land) and China (on land and in the maritime sphere). To counter Chinese influence in the Indo-Pacific, New Delhi will have to work with others – especially the United States. It would not make sense for India to want to weaken the US naval presence in the Indian Ocean.

FDI: Let’s explore some possibilities for resettlement. Were a situation in which BIOT remains under UK jurisdiction, with the Chagossians permitted to return to the other islands (but with Diego Garcia remaining a closed military area), not be a workable compromise?

PH: It might be a workable compromise in the short term, but it is not a sustainable solution and would create more problems than it solved. If a small group of Chagossians resettled the Outer Islands, that might satisfy the United States so long as Diego Garcia was kept off limits. But it would not satisfy Mauritius. Port Louis would still argue (rightly) that its claim over the Chagos Archipelago was as strong as ever. The International Court of Justice’s advisory opinion would not be made any less relevant. The UN General Assembly would be unlikely to budge. In other words, it wouldn’t “buy off” anyone except perhaps a few hundred Chagossians. On the contrary, the presence of a permanent civilian population in any part of the Chagos Archipelago would only lend weight to arguments for decolonisation: Britain would be under pressure to allow the resettled Chagossians to form a representative assembly or otherwise practise self-government. What would happen if the islanders petitioned for Mauritian sovereignty? What if they clashed with the base? What if they appealed to the UN to bring about full decolonisation? The point is that resettlement under British sovereignty might be possible, but it would not be a solution to any of the most important legal or political questions at play.

FDI: Would a similar arrangement, still excluding Diego Garcia, be possible under Mauritian sovereignty?

PH: That is a much more workable solution. If the Chagos Archipelago is returned to Mauritius, then the islands will finally be under the jurisdiction of an undisputed sovereign authority. This means that Mauritius could choose to govern Chagos as it wished (within the confines of its own Constitution). One possibility would be to turn Diego Garcia into an autonomous region of Mauritius, with immigration (resettlement) prohibited. Not much need change for the US presence there. Meanwhile, the Outer Islands could become another (separate) autonomous region or else an integral part of Mauritius proper, with immigration permitted. This is probably the best arrangement that the US could hope for: the entire Chagos Archipelago placed under Mauritian sovereignty, but with an agreement that reserved all or most of Diego Garcia for exclusive military purposes.

FDI: What is the economic potential of the archipelago? If some or all of the islands were to be re-populated (regardless of sovereignty), what standard of living are returnees likely to encounter? Will Mauritius simply end up having to subsidise the livelihoods of those new and returning residents?

PH: There is not much economic potential. Any resettled population could feasibly rely on income from fishing, eco-tourism, and sales of .io domain names. But fishing is currently banned under the terms of the Marine Protected Area enacted by the UK in 2010; this conservation zone would have to be reformed by Mauritius if the Chagossians are ever to earn income from sustainable (“zoned”) fishing. Eco-tourism is a possibility, but would have to be done in a way that the US military approved of. It would have to be small-scale (“luxury”) tourism. And, if Mauritius took over control of BIOT, it is not clear that .io domains would continue to exist. If they did, however, then that might provide a source of revenue (similar to how Tuvalu gains income from the sale of .tv domain names).

FDI: Who will foot the bill for the infrastructure that will be needed to facilitate human habitation on islands that have now been deserted for almost five decades?

PH: Resettlement would most likely have to be paid for by Mauritius. It is remotely possible that the US could provide some funds towards this end in exchange for a say over how resettlement should be pursued in practice. There is also the possibility of international funds, from the UN, for example.

FDI: Although it is some way into the future, and a lot can change between now and then, how do you see matters playing out when the US lease on Diego Garcia next comes up for renewal in 2036?

PH: As you say, it is impossible to know for sure. But my suspicion is that, by 2036, the US will have grown tired of the headaches associated with British sovereignty over Chagos. BIOT is an unpopular, illegal, and unnecessary jurisdiction. I expect that the US will soon come to the realisation that it can best preserve its access to Diego Garcia by accepting Mauritian sovereignty over the entire Chagos Archipelago. Once the US comes to that conclusion, it will be curtains for BIOT. Mauritius, the UK and US all belong on the same side: the side of democracy, decolonisation, and a rules-based international order in the Indo-Pacific. In the end, everyone will agree that decolonisation is the strategic course of action and not just the ethical choice.

FDI: Thank you for sharing your time and knowledge with us today, Peter. Your insights have given us much to think about and we shall look forward to staying in contact as we continue to monitor the developments surrounding the BIOT/Chagos Archipelago. 




About the Interviewee: Dr Peter Harris is assistant professor of political science at Colorado State University. He received his PhD in Government from the University of Texas at Austin. His work on Diego Garcia, the Chagos Islands, and the Chagossians has appeared in African Affairs, Environmental Policy and Law, International Political Sociology, International Politics, Marine Policy, and Review of International Studies. His most recent article in the Journal of Indo-Pacific Affairs makes the argument for why the United States ought to support Mauritian sovereignty over the entire Chagos Archipelago.


[1] Introductory information sourced from and

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