Chagos Islands explainer: Why the UK is pressing to transfer sovereignty over the Chagos Islands to Mauritius. Why it can’t happen without US support. What might happen next.
As I write in my book “Lessons in Diplomacy: Politics, Power and Parties“, ‘in few places is the contrast between “easy-looking path to solution” and “ghastly morass of quicksand” so stark as in the British Overseas Territories.‘
This post was updated in April and September 2026.
Going overboard
‘Ready to go overboard?’ the marine says.
‘Ready.’ I eye the choppy water, studded with coral reefs.
I slip off the RIB – a substantial fast motor boat – and into the water, alongside several marines half my age: big, beefy blokes with names like “Snips”, “Whisky” and “Ginger”. We swim towards land, scrambling over razor-sharp reefs that prevent boats reaching the island. At last we wade ashore on the – currently – uninhabited Île Boddam. It is the largest island of the Salomon atoll in the far north of the British Indian Ocean Territory.
After swimming ashore on Île Boddam, September 2008
Chagos Islands: a new dawn?
In November 2022, under Conservative Prime Minister Rishi Sunak, the British government announced that it would open negotiations with Mauritius about sovereignty over BIOT, the British Indian Ocean Territory or Chagos Islands. No-one took much notice.
On 3 October 2024, under Labour Prime Minister Sir Keir Starmer, the United Kingdom and Mauritius announced in a joint statement “an historic political agreement on the exercise of sovereignty over the Chagos Archipelago“. Commentators, including the leadership of the Conservative party, responded with shock and horror.
The key paragraph of the 3 October 2024 announcement reads:
“Today’s political agreement is subject to the finalisation of a treaty and supporting legal instruments, which both sides have committed to complete as quickly as possible. Under the terms of this treaty the United Kingdom will agree that Mauritius is sovereign over the Chagos Archipelago, including Diego Garcia. At the same time, both our countries are committed to the need, and will agree in the treaty, to ensure the long-term, secure and effective operation of the existing base on Diego Garcia which plays a vital role in regional and global security. For an initial period of 99 years, the United Kingdom will be authorised to exercise with respect to Diego Garcia the sovereign rights and authorities of Mauritius required to ensure the continued operation of the base well into the next century.”
Chagos Islands 1790s-1968
The French first settled the (unpopulated) islands in the late 18th century as part of Mauritius, which is around 2,000 kilometres away (1,250 miles, around the distance from London to St Petersburg). The UK took over in 1814. Both French and British colonists shipped slaves and indentured labours to the islands to build up a coconut oil industry. Some stayed for generations; others rotated in and out as indentured labour, particularly in the 1960s.
During the 1960s, when Mauritius (including the Chagos Islands) was still a British colony, the UK and US began talks to establish a US military base on Diego Garcia. In 1965 the UK separated off the Chagos Islands as “The British Indian Ocean Territory”. When Mauritius became independent on 12 March 1968, “BIOT” remained a British overseas territory. The British government promised that if the islands were ever no longer needed for defence, they would be returned to Mauritius.
The Chagossians
Before the US built their base on the island of Diego Garcia in the far south of the Chagos islands in the early 1970s, the UK removed the entire population then living in the islands to Mauritius and the Seychelles. The UK paid compensation, intended for the people affected. But legal cases over subsequent decades, including emotive testimony from Chagossians, argued for their return. They also argued that the compensation paid was inadequate or had never reached the intended recipients – leading to the UK paying more. Philippe Sands, a lawyer who has championed the cause of the Chagossians, wrote about the case in his book The Last Colony.
A pretty decent Wikipedia summary of the history of BIOT, including its separation from the then-colony of Mauritius in 1965, is here. The expulsion is the subject of a separate Wikipedia piece here. Both reproduce a notorious and much-quoted minute dated 24 August 1966 by Foreign Office official PRH Wright, with an annotation by his colleague DA Greenhill, which makes derogatory remarks about the inhabitants of the islands as “Tarzans and Men Fridays” and a joke about “Birds” too ghastly to summarise. The colonial-era tone of this communication has not helped the British government case over the years.
A visit to the Chagos Islands
I visited the British Indian Ocean Territory in 2006. At the time, I was Director of Overseas Territories in the Foreign Office (FCO). This made me commissioner, or non-resident governor, of BIOT. I had read of the islands in Simon Winchester’s 1985 book Outposts. Like many people, I was sympathetic to the plight of the Chagossians. Earlier in 2006, the FCO had arranged for a group of Chagossians to visit the islands. It was the first time since the 1970s they had been able to return. Opinions differed over whether, if the Chagossians won the case to resettle the outer islands, this would be feasible. I wanted to see for myself.
A memorial on Peros Banhos to the 2006 visit by Chagossians – Photo LT
Could the Chagos islands be resettled?
Leaving aside the legal arguments, my visit left me scratching my head about the practicality of re-establishing any kind of functioning settlement on the outer islands – as opposed, to, say, a holiday resort – without massive subsidies. The islands are minuscule. One of the likeliest spots for a resettlement is the Peros Bahnos atoll. It consists of 32 islets, with a total land area of less than ten square kilometres. The land area of the Salomon atoll is even smaller. They are, like most atolls, low-lying and vulnerable. There is no infrastructure except on Diego Garcia itself, which under present plans will not be open for resettlement. If, say, luxury resorts were to be built, would significant numbers of Chagossians or their descendants want to work in them? The overwhelming majority of workers at the US base on Diego Garcia when I visited in 2006 were from the Philippines and elsewhere, with only a tiny minority of people of Chagossian origin.
None of this means that the British government did not treat the Chagossians shamefully in the past; or that they do not have a powerful legal and moral case for returning. Nor does it mean resettlement is physically impossible, given sufficient funds. But any such resettlement will not be straightforward.
Set against this, the joint statement says: “Mauritius will now be free to implement a programme of resettlement on the islands of the Chagos Archipelago, other than Diego Garcia, and the UK will capitalise a new trust fund, as well as separately provide other support, for the benefit of Chagossians”. Let’s see.
An abandoned church on Île du Coin, Peros Banhos atoll – Photo LT
Chagos Islands: British political debate
In October 2016, the British government under Conservative Prime Minister Theresa May apologised for “The manner in which the Chagossian community was removed from the Territory in the 1960s and 1970s, and the way they were treated.” A year later, in 2017, the UN General Assembly referred the territorial dispute between the UK and Mauritius over the Chagos Islands to the International Court of Justice. In 2019, the ICJ concluded, in a non-binding advisory ruling, that the UK’s separation of the islands from Mauritius in 1965 had not been lawful; and that the UK must transfer them back to Mauritius. Against this background, the UK’s 2022 announcement of negotiations with Mauritius about the Chagos Islands looked sensible.
In July 2024, the Labour Party won the British general election. Rishi Sunak, leader of the Conservative Party, resigned and votes were held for a new party leader. One candidates was James Cleverly, who as Foreign Secretary under Sunak had masterminded the Chagos Island deal. He came top in the third round of voting on 8 October 2024, and looked set to become leader of the party. The 3 October announcement of a deal on the Chagos Islands by the new Labour government dropped right in the middle of this process. After other candidates attacked Cleverly over his support for the Chagos Islands deal, Cleverly came third in the third round on 9 October and was eliminated. Opposition to the Chagos Islands deal was now entrenched as a policy of the Conservative Party – which had initiated it.
Chagos Islands: US position
According to a June 2025 House of Lords report: “The UK government consulted the US government on the final treaty prior to its approval. The US government stated that, following a “comprehensive interagency review”, it had determined that the agreement “secures the long-term, stable, and effective operation of the joint US-UK military facility at Diego Garcia””. This was not surprising: it would have been inconceivable for the UK to do a deal on the future of the islands without US support, given that the entire purpose of BIOT’s existence is to house the US base. The agreement appeared to give the US base a solid long-term basis in international law in the aftermath of the 2019 ICJ ruling.
Chagos Islands: Trump steps in
President Trump took office, for the second time, in January 2025. He, too, appeared to welcome the deal. According to the House of Lords report, Trump “said during a meeting with Sir Keir Starmer in February 2025 that he was “inclined” to go along with the agreement and that he had “a feeling that it’s going to work out very well””. When the deal was signed in May 2025, US Secretary of State Marco Rubio officially welcomed it as a “historic agreement” that secured the base’s long-term operation. Rubio stated that President Trump expressed support for this “monumental achievement“.
There then followed a series of U-turns, highlighted at the previous link. In January 2026, with tension flaring over Trump’s claims on Greenland, Trump suddenly attacked the BIOT deal as an “act of GREAT STUPIDITY”, citing it as “another in a very long line of National Security reasons why Greenland has to be acquired“. In February, Trump switched positions again, calling the deal “the best [PM Starmer] could make“. On 17 February 2026 the US state department stated formally that “The United States supports the decision of the United Kingdom to proceed with its agreement with Mauritius concerning the Chagos archipelago“. But on 18 February – one day later – Trump again attacked the deal, concluding: “the U.K… have to remain strong in the face of Wokeism, and other problems put before them. DO NOT GIVE AWAY DIEGO GARCIA!“
In September 2026, meeting UK Prime Minister Andy Burnham for the first time, President Trump again called the UK’s Chagos deal with Mauritius “terrible”. In response, UK Defence Minister Wes Streeting said that the British government “had to” review the deal “because the United States doesn’t support it”.
What about the money?
Critics of the scheme have argued that the proposed deal would cost the UK money. At first sight, the amounts of money involved certainly look eye-watering. Under the deal, the UK promises to give Mauritius, according to a House of Commons report, “an annual average of £101 million for 99 years in 2025/26 prices, totalling around £3.4 billion”. The government says this figure has been verified by the Government Actuary’s Department.
But looking at that statement, if you tot up £101 million a year for 99 years, adjusted upward for inflation (“in 2025/26 prices”) you get a much bigger number than a mere £3.4 billion. Some estimates put the full cost as high as £35 billion over the 99 years. The reason for the discrepancy is that the government applies a methodology known as “net present value” to future costs, meaning that the value of future spending is discounted when compared to current spending. Thus, future pounds are worth less than current pounds. Either way, the amount the British government proposes to pay Mauritius looks surprisingly high. If anyone knows how the £101m figure was arrived at, please put a link in the comments.
Bizarrely, I have not been able to find any references to whether the US will contribute to the £3.4 billion or £35 billion cost of the deal with Mauritius. Under the set-up as-is, BIOT costs the UK taxpayer money without generating any income. This is true of most Overseas Territories. But the costs of the Chagos Islands to the UK are relatively modest – this article suggests in the order of hundreds of thousands of pounds a year, rather than hundreds of millions.
The US does has not in the past paid “rent” for use of the military base on Diego Garcia, perhaps on the grounds that the costs to the UK were modest. If the costs are set to rise massively under the 2025 deal with Mauritius, it would be interesting to know whether the UK has proposed that the US should in future contribute more; and, if not, why not. Again, if anyone has seen any public discussion of this, please put a link in the comment.
A risk to the US military?
The British government must have been conscious that past governments had argued that UK sovereignty over BIOT was vital for the base on Diego Garcia. On 3 October 2024, they released an additional statement. It argued that the deal would strengthen, rather than weaken, the legal basis of the US-run base. “For the first time in more than 50 years,” it said, “the status of the base will be undisputed and legally secure, following a political agreement between the UK and Mauritius.” This sounded plausible, pending sight of the “treaty and supporting legal instruments” described in the joint statement.
The impact of the proposed deal on the military value of the US base would depend on the details. It is not clear whether the deal placed any restrictions on military use of the “outer islands” of BIOT. These include the Egmont Islands (depopulated in the 1930s); the Peros Banhos atoll; and the Salomon atoll. The latter were both depopulated as part of the removals of the 1970s. They are the likeliest spots for any resettlement. Geography is important. BIOT is a group of atolls about 230 km from north to south and a bit over half as wide. Peros Banhos and the Salomons are around 230 km away from Diego Garcia, Egmont Island around 140 km. Diego Garcia is the closest significant island to Mauritius, which is around 2,000 km away.
It is open to debate whether civilian resettlement of the outer islands would affect the military value of Diego Garcia. Military use of the outer islands by a hostile power would be another matter. It has at no stage seemed likely that any agreement between the UK and Mauritius would allow this. But I have not managed to track down any documentation on this. Again I’d welcome any further information on whether the agreement specifically rules it out.
Should the Chagossians have been consulted?
Chagossians gave a mixed response to the 2024 deal. At the time The Guardian, which has long campaigned for the Chagossians, reported Olivier Bancoult, chair of the Chagos Refugee Group, as welcoming it. But he added that “if Mauritius will not fulfil its responsibilities to us, of course we will raise our voices.” Others complained no-one had consulted them. I wrote in 2024 that “We can expect continued criticism of the October 2024 announcement from those who feel it disadvantages them”. This has, indeed, happened.
An abandoned cemetery on Peros Banhos – Photo LT
Chagos Islands: a future source of conflict?
Bancoult’s challenge over whether Chagossians will actually be able to resettle the islands highlights a potential future source of conflict. Will the Chagossians want to resettle the outer islands under the terms of the agreement? Will the Mauritians, once they regain sovereignty, allow or encourage this? What if other Mauritians – far more numerous than the Chagossians and their descendants – want to settle there?
Bancoult’s comments also highlight the advantages of the deal to London. People will always accuse the UK – in many cases correctly – of historic colonial misdeeds. But if and when sovereignty is transferred, the resettlement of the outer Chagos islands will be for the government of Mauritius, not the UK, to decide.
Similarly, I was struck by a statement by then-Foreign Secretary David Lammy, reported in the Guardian of 7 October 2024. He was asked about the fate of over 60 Tamil refugees stranded on the island of Diego Garcia for years. Lammy replied: “On signing the treaty this is now a matter for Mauritius.” This looks like a key underlying reason for the UK being prepared to countenance the transfer of sovereignty over BIOT: to reduce by one the number of overseas territories and the complex moral and policy issues they constantly seem to generate.
Some elements of the UK political spectrum may feel that the possession of overseas territories somehow bolsters the UK’s international status. Practical benefits to the UK, however, are difficult to identify. By contrast, the case of the Chagos Islands illustrates the immense potential costs and contingent liabilities the OTs represent. If anyone would like to set out the practical or financial benefits to the UK of the overseas territories, please do so in the comments.
Does the deal have implications for other Overseas Territories?
In short, no. The circumstances of each British Overseas Territory are unique. Some, such as Gibraltar and the Falklands, are subject to territorial disputes. People living in both are passionate about remaining under the wing of the UK. Others, such as Pitcairn, are too small to be independent. Still others, like the Cayman Islands and Bermuda, could be independent tomorrow if they wanted to, but prefer the status quo. Arguments will rumble on. But there is little crossover between the issues affecting the individual OTs.
The Chagos Islands: in summary
I personally thought the deal announced in 2024 was good news. My 2024 book “Lessons in Diplomacy: Politics, Power and Parties“, has a chapter about Britain’s Overseas Territories. It is entitled “How to grapple with a legacy of colonialism”. I noted optimistically the opening of negotiations on the Chagos Islands in 2022. But I also pointed out that the OTs are famous for generating complex problems. ‘In few places,’ I write, ‘is the contrast between “easy-looking path to solution” and “ghastly morass of quicksand” so stark as in the British Overseas Territories.‘
The depth and tenacity of that quicksand has been illustrated once again by the fallout of the 2024 deal. At the time, I wrote: “The Chagos Islands deal announced on 3 October solves a lot of problems. It will, no doubt also create new ones. Let us hope they are lesser ones.” The latest developments highlight the new problems created. They also show the challenges of negotiating with President Trump.
What next?
Any issue as loaded with historical burdens as this will inevitably leave many people unhappy or enraged. That includes some of those who have campaigned to return to live on the islands. In the past, Mauritius and its supporters excelled in putting pressure on the British government. Now, the pausing of the deal is demonstrably due to US opposition. It would be logical for Mauritius now to start a campaign of pressure on Washington. Let’s see.
The military base on Diego Garcia is not a US/UK base. It is a US base with a handful of UK service personnel whose primary responsibility is to exercise UK sovereignty. Because of the importance of Diego Garcia, it is true that the UK cannot go ahead with the Mauritius deal without US support. As of September 2026, I would expect that any review the UK may undertake will not reach any conclusion while Trump remains president. Nor would I expect Mauritius to mount a determined campaign to change the US position while Trump remains in office. Meanwhile, the UK is potentially saving £101 million a year.
If Mauritius ever does regain sovereignty over the Chagos Islands, a key question will be whether the government in Port Louis allows Chagossians to resettle. Possible sites might be Île du Coin, Île Boddam or elsewhere in the outer islands. My perception is that the Mauritian authorities would not particularly welcome this. Some Chagossians, perhaps including some living in the UK, may fear that it will be harder to influence or exert political pressure on the government of Mauritius than it is to influence the British government. Resettling the islands (see above) is challenging. There are no easy ways forward – with our without the deal negotiated between the UK and Mauritius in 2024.
Lessons in Diplomacy has a chapter on the British Overseas Territories
