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Chagos Archipelago sovereignty dispute

Dispute between Mauritius and the United Kingdom

The meetings culminated in the afternoon of 23 September 1965 (the "Lancaster House Meeting") in a provisional agreement on the part of Sir Seewoosagur Ramgoolam and his colleagues to agree in principle to the detachment of the Archipelago in exchange for the Secretary of State recommending certain actions by the United Kingdom to the Cabinet. The draft record of the Lancaster House Meeting set out the following:

(i) negotiations for a defence agreement between Britain and Mauritius;
(ii) in the event of independence an understanding between the two governments that they would consult together in the event of a difficult internal security situation arising in Mauritius;
(iii) compensation totalling up to [illegible] Mauritius Government over and above direct compensation to landowners and the cost of resettling others affected in the Chagos Islands;
(iv) the British Government should use its good offices with the United States Government in support of Mauritius’ request for concessions over sugar imports and the supply of wheat and other commodities;
(v) that the British Government would do their best to persuade the American Government to use labour and materials from Mauritius for construction work in the islands;
(vi) that if the need for the facilities on the islands disappeared the islands should be returned to Mauritius. Seewoosagur Ramgoolam said that this was acceptable to him and Messrs. Bissoondoyal and Mohamed in principle but he expressed the wish to discuss it with his other ministerial colleagues.}}

Thereafter, Sir Seewoosagur Ramgoolam addressed a handwritten note to the Under-Secretary of State at the Colonial Office, Mr Trafford Smith, setting out further conditions relating to navigational and meteorological facilities on the Archipelago, fishing rights, emergency landing facilities, and the benefit of mineral or oil discoveries.

On 6 October 1965, instructions were sent to the Governor of Mauritius to secure "early confirmation that the Mauritius Government is willing to agree that Britain should now take the necessary legal steps to detach the Chagos Archipelago from Mauritius on the conditions enumerated in (i)–(viii) in paragraph 22 of the enclosed record [of the Lancaster House Meeting]." The Secretary of State went on to note that -

As regards points (iv), (v) and (vi) the British Government will make appropriate representation to the American Government as soon as possible. You will be kept fully informed of the progress of these representations.
The Chagos Archipelago will remain under British sovereignty, and Her Majesty’s Government have taken careful note of points (vii) and (viii).}}

On 5 November 1965, the Governor of Mauritius informed the Colonial Office as follows:

Council of Ministers today confirmed agreement to the detachment of Chagos Archipelago on conditions enumerated, on the understanding that

(1) statement in paragraph 6 of your despatch "H.M.G. have taken careful note of points (vii) and (viii)" means H.M.G. have in fact agreed to them.

(2) As regards (vii) undertaking to Legislative Assembly excludes (a) sale or transfer by H.M.G. to third party or (b) any payment or financial obligation by Mauritius as condition of return. (3) In (viii) "on or near" means within area within which Mauritius would be able to derive benefit but for change of sovereignty. I should be grateful if you would confirm this understanding is agreed.}}

The Governor also noted that "Parti Mauricien Social Démocrate (PMSD) Ministers dissented and (are now) considering their position in the government." The Parties differ regarding the extent to which Mauritian consent to the detachment was given voluntarily.

The detachment of the Chagos Archipelago was effected by the establishment of the British Indian Ocean Territory (BIOT) on 8 November 1965 by Order in Council. Pursuant to the Order in Council, the governance of the newly created BIOT was made the responsibility of the office of the BIOT Commissioner, appointed by the Queen upon the advice of the United Kingdom FCO. The BIOT Commissioner is assisted in the day-to-day management of the territory by a BIOT Administrator.

On the same day, the Secretary of State cabled the Governor of Mauritius as follows:

On 12 November 1965, the Governor of Mauritius cabled the Colonial Office, querying whether the Mauritian Ministers could make public reference to the items in paragraph 22 of the record of the Lancaster House Meeting and adding "[i]n this connection I trust further consideration promised . . . will enable categorical assurances to be given."

On 19 November 1965, the Colonial Office cabled the Governor of Mauritius as follows: U.K./U.S. defence interests;

It may well be some time before we can give final answers regarding points (iv), (v) and (vi) of paragraph 22 and as you know we cannot be at all hopeful for concessions over sugar imports and it would therefore seem unwise for anything to be said locally which would raise expectations on this point.
As regards point (vii) the assurance can be given provided it is made clear that a decision about the need to retain the islands must rest entirely with the United Kingdom Government and that it would not (repeat not) be open to the Government of Mauritius to raise the matter, or press for the return of the islands on its own initiative.
As stated in paragraph 2 of my telegram No. 298 there is no intention of permitting prospecting for minerals and oils. The question of any benefits arising therefrom should not [. . .] [illegible]7 There is no objection to Ministers referring to points contained in paragraph 22 of enclosure to Secret despatch No. 423 of 6 October so long as qualifications contained in paragraphs 5 and 6 of the despatch are borne in mind. 2. It may well be some time before we can give final answers regarding points (iv), (v) and (vi) of paragraph 22 and as you know we cannot be at all hopeful for concessions over sugar imports and it would therefore seem unwise for anything to be said locally which would raise expectations on this point. 3. As regards point (vii) the assurance can be given provided it is made clear that a decision about the need to retain the islands must rest entirely with the United Kingdom Government and that it would not (repeat not) be open to the Government of Mauritius to raise the matter, or press for the return of the islands on its own initiative.}}

A few weeks after the proposal to detach the islands from Mauritius, the United Nations General Assembly passed Resolution 2066(XX) on 16 December 1965, which stated that detaching part of a colonial territory was against customary international law and the UN Resolution 1514 passed on 14 December 1960. This resolution stated that "Any attempt aimed at the partial or total disruption of the national unity and the territorial integrity of a country is incompatible with the purposes and principles of the Charter of the United Nations."

Depopulation

Main article: Expulsion of the Chagossians

After initially denying that the islands were inhabited, British officials forcibly expelled approximately 2,000 Chagossians to mainland Mauritius to allow the United States to establish a military base on Diego Garcia. Since 1971, the atoll of Diego Garcia is inhabited by some 3,000 UK and US military and civilian contracted personnel. The British and American governments routinely deny Chagossian requests for the right of return.

Marine protected area

Main article: Chagos Marine Protected Area

A marine protected area (MPA) around the Chagos Islands known as the Chagos Marine Protected Area was created by the British Government on 1 April 2010 and enforced on 1 November 2010. It is the world's largest official reserve, twice the size of Great Britain. The designation proved controversial as the decision was announced during a period when the UK Parliament was in recess. Despite the official designation as a marine reserve, the US military is fully exempt from fishing restrictions and the military base has been a major source of pollution to the area.

A leaked diplomatic cable dating back to 2009 reveal the British and US role in creating the marine nature reserve. The cable relays exchanges between US Political Counselor Richard Mills and British Director of the Foreign and Commonwealth Office Colin Roberts, in which Roberts "asserted that establishing a marine park would, in effect, put paid to resettlement claims of the archipelago's former residents." Richard Mills concludes:Establishing a marine reserve might, indeed, as the FCO's Roberts stated, be the most effective long-term way to prevent any of the Chagos Islands' former inhabitants or their descendants from resettling in the [British Indian Ocean Territory].

Resettlement study

In March 2014, it was reported that the UK government would send experts to the islands to examine "options and risks" of resettlement.

Legal proceedings

Case before Permanent Court of Arbitration

Main article: Mauritius v United Kingdom

The Government of Mauritius initiated proceedings on 20 December 2010 against the UK Government under the United Nations Convention on the Law of the Sea (UNCLOS) to challenge the legality of the ‘marine protected area’. Mauritius argues that Britain breached a UN resolution when it separated Chagos from the rest of the colony of Mauritius in the 1960s, before the country became independent, and that Britain therefore doesn't have the right to declare the area a marine reserve and that the MPA was not compatible with the rights of the Chagossians. The dispute was arbitrated by the Permanent Court of Arbitration. The sovereignty of Mauritius was explicitly recognized by two of the arbitrators and denied by none of the other three. Three members of the Tribunal found that they did not have jurisdiction to rule on that question; they expressed no view as to which of the two States has sovereignty over the Chagos Archipelago. Tribunal Judges Rüdiger Wolfrum and James Kateka held that the Tribunal did have jurisdiction to decide this question, and concluded that UK does not have sovereignty over the Chagos Archipelago. They found that:

internal United Kingdom documents suggested an ulterior motive behind the MPA, noting disturbing similarities and a common pattern between the establishment of the so-called "BIOT" in 1965 and the proclamation of the MPA in 2010;
the excision of the Chagos Archipelago from Mauritius in 1965 shows a complete disregard for the territorial integrity of Mauritius by the UK;
UK Prime Minister Harold Wilson's threat to Premier Sir Seewoosagur Ramgoolam in 1965 that he could return home without independence if he did not consent to the excision of the Chagos Archipelago amounted to duress; Mauritian Ministers were coerced into agreeing to the detachment of the Chagos Archipelago, which violated the international law of self-determination;
the MPA is legally invalid.

On 18 March 2015, the Permanent Court of Arbitration ruled that the Chagos Marine Protected Area was illegal. The Tribunal's decision determined that the UK's undertaking to return the Chagos Archipelago to Mauritius gives Mauritius an interest in significant decisions that bear upon possible future uses of the archipelago. The result of the Tribunal's decision is that it is now open to the Parties to enter into the negotiations that the Tribunal would have expected prior to the proclamation of the MPA, with a view to achieving a mutually satisfactory arrangement for protecting the marine environment, to the extent necessary under a "sovereignty umbrella".

International Court of Justice

Amendment of exclusion clause by UK

In 2004, following the decision of the British government to promulgate the British Indian Ocean Territory Order, which prohibited the Chagossians from remaining on the islands without express authorisation, Mauritius contemplated recourse to the International Court of Justice to finally and conclusively settle the dispute. However, article 36 of the International Court of Justice Statute provides that it is the option of the state whether it wishes to subject itself to the court's jurisdiction. Where the state chooses to be so bound, it may also restrict or limit the jurisdiction of the court in a number of ways. The UK's clause deposited at the court excluded, amongst other things, the jurisdiction of the court with regard "to any disputes with the government of any country which is a member of the Commonwealth with regard to situations or facts existing before 1 January 1969". The temporal limitation of 1 January 1969 was inserted to exclude all disputes arising during decolonisation. The effect of the British exclusionary clause would thus have prevented Mauritius from resorting to the court on the Chagos dispute because it is a member of the Commonwealth. When Mauritius threatened to leave the Commonwealth, the United Kingdom quickly amended its exclusion clause to exclude any disputes between itself, Commonwealth States and former Commonwealth States, thereby quashing any Mauritian hopes to ever have recourse to the contentious jurisdiction of the court, even if it left.

Advisory opinion

On 23 June 2017, the United Nations General Assembly (UNGA) voted in favour of referring the territorial dispute between Mauritius and the UK to the International Court of Justice (ICJ) in order to clarify the legal status of the Chagos Islands archipelago in the Indian Ocean. The motion was approved by a majority vote with 94 voting for and 15 against. In September 2018, the International Court of Justice began hearings on the case. Seventeen countries have argued in favour of Mauritius. The UK apologised for the "shameful" way islanders were evicted from the Chagos Archipelago but were insistent that Mauritius was wrong to bring the dispute over sovereignty of the strategic atoll group to the United Nations' highest court. The UK and its allies argued that this matter should not be decided by the court but should be resolved through bilateral negotiations, while bilateral discussions with Mauritius have been unfruitful over the past 50 years.

On 25 February 2019, the judges of the International Court of Justice by thirteen votes to one stated that the United Kingdom is under an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible. Only the American judge, Joan Donoghue, voted in favor of the UK. The president of the court, Abdulqawi Ahmed Yusuf, said the detachment of the Chagos Archipelago in 1965 from Mauritius had not been based on a "free and genuine expression of the people concerned". "This continued administration constitutes a wrongful act", he said, adding "The UK has an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible and that all member states must co-operate with the United Nations to complete the decolonization of Mauritius." Largely because of the detachment of the islands, the ICJ determined that the decolonization of Mauritius was still not lawfully completed. On 1 May 2019, the UK Foreign Office minister Alan Duncan stated that Mauritius has never held sovereignty over the archipelago and the UK does not recognise its claim. He stated that the ruling was merely an advisory opinion and not a legally binding judgment. Jeremy Corbyn, leader of the UK's main opposition party, wrote to the UK PM condemning her decision to defy a ruling of the UN's principal court that concluded that Britain should hand back the Chagos Islands to Mauritius. He expressed his concern that the UK government appears ready to disregard international law and ignore a ruling of the international court and the right of the Chagossians to return to their homes.

Legal consequences

While the UN advisory opinion and resolutions are not legally binding, it carries significant political weight since the ruling came from the UN's highest court and the assembly vote reflects world opinion. The ruling of the ICJ would be similar if the UK agreed to go for a contentious case. The resolution also has immediate practical consequences: the UN, its specialised agencies, and all other international organisations are now bound, as a matter of UN law, to support the decolonisation of Mauritius even if the UK continue to claim that it has no doubt about its sovereignty.

UN Resolution

On 22 May 2019, the United Nations General Assembly debated and adopted a resolution that affirmed that the Chagos Archipelago, which has been occupied by the UK for more than 50 years, "forms an integral part of the territory of Mauritius". The resolution gives effect to an advisory opinion of the International Court of Justice (ICJ), demanded that the UK "withdraw its colonial administration ... unconditionally within a period of no more than six months". 116 states voted in favour of the resolution, 55 abstained and only Australia, Hungary, Israel and Maldives supported the UK and US. During the debate, the Mauritian Prime Minister described the expulsion of Chagossians as "a crime against humanity". China abstained in the 2019 UN vote, which was a step towards reaching an agreement to return the Chagos Archipelago to Mauritius.

Changes in official UN Maps

Updated UN Map Map No. 4170 Revision 18.1 depicting the Chagos Archipelago as Mauritian Territory

Following the International Court of Justice (ICJ) advisory opinion in 2019 and the subsequent United Nations General Assembly (UNGA) resolution, several international organizations updated their official maps to reflect Mauritius' sovereignty over the Chagos Archipelago. The United Nations (UN), in compliance with the UNGA resolution, amended its official map on 20 February 2020 with Map No. 4170 Revision 18.1, recognizing the Chagos Islands as part of Mauritius instead of British territory.

Case before International Tribunal for the Law of the Sea

The Maldives is involved in a dispute with Mauritius regarding the boundaries of their respective Exclusive Economic Zones (EEZs), particularly in relation to the EEZ of the Chagos Archipelago. In June 2019, Mauritius initiated arbitral proceedings against the Maldives at the International Tribunal for the Law of the Sea (ITLOS) to resolve the maritime boundary between the Maldives and the Chagos Archipelago. Among its preliminary objections, the Maldives argued that a sovereignty dispute existed between Mauritius and the United Kingdom over the Chagos Archipelago, and that this issue fell outside ITLOS's jurisdiction. On 28 January 2021, ITLOS ruled that the sovereignty dispute between the United Kingdom and Mauritius had already been definitively addressed through the International Court of Justice's (ICJ) earlier Advisory Opinion, which affirmed that the United Kingdom has no sovereignty over the Chagos Archipelago. Consequently, ITLOS declared there was no jurisdictional barrier, dismissing all five of the Maldives' preliminary objections and accepting Mauritius' claims as admissible.

Universal Postal Union banned BIOT stamps

The Universal Postal Union (UPU), a UN specialized agency for postal matters, officially recognized the Chagos Archipelago as part of Mauritius on 27 August 2021. The decision was made during the 27th Universal Postal Congress in Abidjan, Côte d'Ivoire, with 77 votes in favor, 6 against, and 41 abstentions. As a result, the UPU will no longer register, distribute, or forward postage stamps from the "British Indian Ocean Territory," which previously included the Chagos Archipelago. This follows the 2019 UN General Assembly directive, based on advice from the International Court of Justice, affirming Mauritius' sovereignty over the archipelago. The UPU, as a UN agency, is required to align with UN decisions, bringing the matter to its governing body for resolution. All post from the Chagos Islands must now bear stamps from Mauritius and stamps marked British Indian Ocean Territory now will not be recognised.

Amendment to Mauritius Criminal Code

Section 76B of the Criminal Code in Mauritius was introduced through the Criminal Code (Amendment) Act 2021, which was amended on 26 November 2021. This provision aims to protect Mauritius’ territorial integrity by criminalizing actions that misrepresent its sovereignty over any part of its territory.

The law applies to individuals acting under the authority, instructions, or financial support (direct or indirect) of a foreign state. Offenses include:

Producing, distributing, or marketing coins, stamps, maps, or official documents that misrepresent Mauritius' sovereignty.
Instructing others to engage in such activities.

A "foreign state" under this provision refers to any country that an international court or tribunal has determined to have no valid claim over any part of Mauritius' territory. Persons found guilty of violating this law may face:

A fine of up to 5 million Mauritian rupees
Imprisonment for up to 10 years

The law applies extraterritorially, meaning that offenses committed outside Mauritius are still considered as having been committed within the country. The Intermediate Court has jurisdiction over such cases and can impose the prescribed penalties.

UK's status in the Indian Ocean Tuna Commission

In May 2022, the Food and Agriculture Organization issued a legal opinion asserting that the United Kingdom should no longer be recognized as a "coastal state" in the Indian Ocean, due to the disputed status of the Chagos Archipelago. This position follows UN General Assembly resolution 73/295, which affirms the Chagos Archipelago as part of Mauritius. Consequently, the UK is now considered a state that fishes in the region but does not hold the rights or obligations of a coastal state under the Indian Ocean Tuna Commission framework.

2022–2025 negotiations

On 3 November 2022, the Secretary of State for Foreign, Commonwealth and Development Affairs, James Cleverly, stated that the United Kingdom and Mauritius had committed to negotiating an agreement based on international law to resolve outstanding issues, including those concerning the former inhabitants of the Chagos Archipelago. This agreement aims to strengthen bilateral cooperation on regional and global security challenges, particularly in the Indian Ocean. Key areas of focus include maritime security, environmental conservation, climate change, human rights, and efforts to combat illegal migration, fishing, drug, and arms trafficking. Cleverly also reaffirmed that any agreement would ensure the continued effective operation of the joint UK-US military base on Diego Garcia, recognizing its strategic importance. The negotiations will also consider the interests of key regional partners, including the United States and India. The UK and Mauritius have agreed to engage in constructive discussions with the goal of reaching an agreement by early next year.

On 3 October 2024, the UK and Mauritius issued a joint statement, affirming Mauritius' sovereignty over the Chagos Archipelago while granting the UK continued control over Diego Garcia for 99 years. This agreement implicitly indicates that the UK will maintain sovereignty over Diego Garcia, which hosts a critical military base. Additionally, provisions for Chagossians, regional security, and environmental cooperation are included, strengthening bilateral ties between the two nations.

In his October 2024 statement on the Chagos Islands, Foreign Secretary David Lammy discussed the contested status of the territory and the UK-US military base. He emphasized the unsustainability of the status quo and the inevitability of a binding judgment against the UK. Lammy acknowledged the only viable path was negotiating a deal to ensure the base's continued operation and international law compliance, avoiding the choice of abandoning the base or breaking international law.

After the general elections in Mauritius, Navin Ramgoolam became the Prime Minister on 13 November 2024. Upon assuming office, Ramgoolam received a letter from British Prime Minister Keir Starmer on 12 November 2024, informing him of plans to send British political envoy Jonathan Powell to Mauritius. On 25 November 2024, Powell arrived in Mauritius and briefed the Prime Minister on the current status of the agreement. During the meeting, the Prime Minister expressed surprise that the agreement had been made shortly before the dissolution of Parliament, with the opposition being unaware of the negotiations.

On 20 December 2024, the UK and Mauritius issued a joint statement outlining their commitment to resolving the sovereignty dispute over the Chagos Archipelago. The agreement will transfer sovereignty to Mauritius while preserving the operations of the Diego Garcia military base. Both nations have pledged to complete the treaty process promptly.

Following Powell's visit, the Prime Minister ordered an independent review of the confidential draft agreement. The document, which had been presented to the new Mauritian government after the 2024 general elections, was unknown to the officials before the change in leadership. This review was conducted by an inter-ministerial committee comprising the Deputy Prime Minister, Attorney General, and Minister of Foreign Affairs, Regional Integration, and International Trade.

A senior delegation from the United Kingdom visited Mauritius from 9–12 December 2024 to engage in further discussions. While meetings were held between the senior officials of both countries, the UK delegation also met with the Prime Minister to discuss the specifics of the draft agreement. Mauritius expressed its willingness to conclude an agreement but made it clear that the draft presented did not meet the nation's expectations. The government proposed counterproposals to the United Kingdom, seeking to negotiate terms that were more favourable to Mauritius.

On 16 December 2024, the United Kingdom responded to Mauritius' counterproposals. These responses were considered by the inter-ministerial committee, which led to a further exchange of proposals. On 31 December 2024, Mauritius submitted its final response and suggested a meeting in London to finalize the agreement.

On 13 January 2025, the governments of the UK and Mauritius issued a joint statement regarding the Chagos Archipelago. They affirmed progress in their discussions, working towards a treaty that would establish Mauritius as the sovereign authority over the archipelago while ensuring the continued operation of the Diego Garcia base. The talks are ongoing, aiming to reach a mutually beneficial agreement.

On 15 January 2025, a special Cabinet meeting was convened to discuss the progress of the negotiations. However, before the meeting, Mauritius was informed by the UK that, in light of the imminent change in the United States administration, they would await the views of the new US administration before finalizing the agreement. Despite this, a delegation from Mauritius, led by the Attorney General, travelled to the UK on 16–17 January 2025 to continue discussions. During these meetings, UK officials, including Lord Hermer and Under Secretary of State Stephen Doughty, reassured the Mauritian delegation of the UK's commitment to signing the agreement. The Mauritian government expressed strong concerns about the draft agreement proposed by the UK, citing several key issues that needed to be addressed:

Sovereignty: The agreement failed to clearly affirm full sovereignty over the Chagos Archipelago, including Diego Garcia.
Duration and Renewal: The agreement proposed a 99-year term, with the UK having the unilateral right to extend the agreement for an additional 40 years without Mauritian input.
Economic Terms: The financial terms of the agreement were criticized for being poorly negotiated, with inflation and currency exchange rates not adequately factored in.

The Mauritian government rejected the draft, arguing that it was a “sell-out” and that the terms would not benefit the nation in the long term. The Prime Minister insisted that the agreement needed to be renegotiated to secure better terms for Mauritius. The British Prime Minister, in a telephone conversation with the Prime Minister of Mauritius on 2 February 2025, indicated that the UK government intended to proceed with the agreement on the Chagos Archipelago. While the agreement had reached a near-final stage, the UK's decision to wait for the new US administration's views delayed the signing. However, the Mauritian government remained confident that a resolution would be reached shortly, with the Prime Minister stating that negotiations would continue with the aim of securing a mutually beneficial agreement.

On 5 February 2025, Stephen Doughty, the Minister of State for Europe, North America and Overseas Territories, emphasized that international legal rulings have cast doubt on Britain's sovereignty over the Chagos Islands, making a deal with Mauritius crucial to ensuring the continued operation of the US military base on Diego Garcia. He highlighted the UK's control over the electromagnetic spectrum used for satellite communications, governed by the International Telecommunication Union, noting that while Britain could still communicate without it, others could also use the spectrum, threatening the base's security. Doughty further outlined the UK's full control over Diego Garcia, including a buffer zone and mechanisms to prevent interference, underscoring that a future deal with Mauritius would secure the base's operations and national security, free from external risks.{{cite Hansard |speaker=Farage, Nigel; Doughty, Stephen |house=House of Commons|position=The Minister of State, Foreign, Commonwealth and Development Office|url=https://hansard.parliament.uk/commons/2025-02-05/debates/764272BD-61D6-44C8-9DC2-E41EDF891AC6/ChagosIslands|title=Chagos Islands |column=753 |volume=761

On 27 February 2025, speaking in the Oval Office alongside Prime Minister Keir Starmer, U.S. President Donald Trump stated that he was willing to support the agreement to transfer sovereignty of the Chagos Islands to Mauritius. Ramgoolam described Trump's comments as seeming positive, but said the Mauritian government would still need to wait to see Britain's final proposals. The Daily Telegraph reported on 2 March 2025 that according to a senior source, Trump's public statements were taken as the approval the British government had been waiting for to continue making progress, and that the UK and Mauritius were expected to finalise the deal as early as 4 March, although the formal endorsement of the U.S. would be required before it could be finalised and signed. On 1 April 2025, U.S. President Donald Trump approved the deal between the UK and Mauritius. However, the Maldives opposed the deal stating that it and the Chagos are connected through historical means.

On 22 May 2025, Mauritius and the United Kingdom formally signed the agreement to hand sovereignty over to Mauritius. The agreement requires ratification by both parties before it can go into effect.

On 25 June 2025, the peers of the House of Lords concluded that the government "cannot ignore" the risk of an "adverse decision" jeopardizing Great Britain's right to operate a joint American and British base.

The agreement may be renewed for an additional 40 years after the initial 99-year period, and for an additional period thereafter.

In July 2025, a legal action demanding that the British government consult with the Chagossians before transferring sovereignty of their territory progressed before the High Court. The judicial review, initiated by Chagossian claimant Louis Misley Mandarin with the support of the Great British PAC, was accepted and fast-tracked by the High Court, with a decision set for July 2025.

Following the Chagos Archipelago handover agreement, the British government is also due to introduce legislation to implement the agreement, including amending the British Nationality Act 1981 to reflect that the British Indian Ocean Territory is no longer an overseas territory following Parliament's ratification of the treaty, and to empower the British government to make secondary legislation to allow for the continued operation of the Diego Garcia military base.

Reaction to 2025 agreement

Support

The United States supported the deal. In a press statement dated 22nd May 2025, Secretary of State Marco Rubio said, "Today, the United States welcomed the historic agreement between the United Kingdom and the Republic of Mauritius on the future of the British Indian Ocean Territory—specifically, the Chagos Archipelago." He went on to confirm that the Trump administration had determined that the long-term operation of the base on Diego Garcia was secure, describing that facility as "a critical asset for regional and global security" and mentioning that President Trump also "expressed his support for this monumental achievement". On May 23, 2025, India welcomed the agreement between the United Kingdom and Mauritius for the transfer of sovereignty over the Chagos Islands, describing it as an important step in completing the decolonization of the island nation "in the spirit of international law and a rules-based order". On May 29, 2025, a roundtable took place in Mauritius. The debate at this roundtable was to develop a program that would allow a Mauritian delegation to travel to the Chagos Archipelago to raise the Mauritian flag. This will be a symbolic step toward finalizing the restitution agreement with Great Britain.

Chagossian population, representation, and political divisions

Population distribution and representation

The majority of Chagossians, including most native-born Chagossians, live in Mauritius, primarily in and around Port Louis. Smaller communities reside in Seychelles and several thousand in the United Kingdom, following changes to UK nationality law that allowed descendants of displaced Chagossians to claim British citizenship.

In Mauritius, many Chagossians are represented by the Chagos Refugees Group (CRG), led by Olivier Bancoult, which advocates for rights of return, compensation, and has publicly supported the UK–Mauritius agreement, considering Mauritian administration consistent with international legal rulings.

Chagossian communities in Seychelles have also expressed support for the treaty, with the Chagos Community of Seychelles, led by Pierre Prosper, describing the agreement between the UK and Mauritius as representing hope for eventual reinstallation and access to the islands under Mauritian administration and recognition of injustices suffered by their community.

UK-based political opposition and self-determination debate

Several UK-resident Chagossians have organised politically to contest aspects of the UK–Mauritius agreement, advocating for what they consider distinct Chagossian interests and a separate voice in decisions regarding the archipelago. Some have established a self-described Chagossian Government-in-Exile and elected Misley Mandarin as leader through online polling; this body is not recognised by any government or international authority.

UK-based opponents have publicly criticised the UK–Mauritius agreement on financial, sovereignty, and political grounds.

Some UK politicians have suggested the deal could cost £35 billion over its lifetime, without clarifying that this figure applies over a 99‑year period, and critics allege Mauritius could use these funds to reduce domestic taxes. Supporters have replied that the annual cost of roughly £101 million is less than the yearly running cost of a UK aircraft carrier, as noted by Prime Minister Keir Starmer in defence of the agreement.

Within this community, there are internal divisions over representation and legitimacy. According to Olivier Bancoult, some opponents in the UK are third or fourth-generation Chagossians born in Mauritius rather than first-generation “déracinés” (uprooted islanders), raising debate about which group most legitimately represents the community.

Some UK-based critics argue that Chagossians should have the same right to a referendum as Gibraltarians or Falkland Islanders, who have voted on sovereignty while living on their territories. Government and legal advisers have stated that a separate referendum is not legally feasible, because Chagossians as a dispersed diaspora do not constitute a distinct territorial population under international law; self-determination rights apply to the entire population of Mauritius.

Some UK-based critics also claim Mauritius “sold” the islands to achieve independence and that Mauritius’s economic development occurred at the expense of Chagossians. Supporters of the treaty reject these claims, viewing them as political opinions rather than legally relevant facts.

Geopolitical and financial criticisms

Some UK critics raised concerns about geopolitical implications, including potential relations between Mauritius and major powers such as China. Proponents emphasised treaty clauses restricting foreign military bases on the islands.

Opponents also raised financial concerns, citing nominal costs over the 99-year leaseback of Diego Garcia; government calculations using net present value indicated the effective cost is roughly equivalent to the annual operating cost of an aircraft carrier.

UK Parliamentary debate and legal issues

Reasons for returning the Chagos Islands

According to UK government statements and parliamentary debate, the transfer of sovereignty to Mauritius was motivated by legal, diplomatic, and strategic factors, including:

Compliance with the 2019 ICJ advisory opinion declaring UK administration unlawful;
Avoiding further international legal rulings that could affect the UK’s position;
Securing the long-term operation of the US–UK military base on Diego Garcia;
Supporting welfare, economic, and infrastructure projects for Chagossians;
Strengthening maritime security and environmental cooperation in the Indian Ocean.

Parliamentary scrutiny and operational risks

The House of Lords debated the treaty, emphasising the need to safeguard airspace, maritime zones, and communications infrastructure around Diego Garcia. Members highlighted that a negotiated settlement was preferable to prolonged litigation or unilateral action.

International legal rulings

In 2015, the Permanent Court of Arbitration (UNCLOS Arbitral Tribunal) ruled that the UK’s unilateral creation of a Marine Protected Area (MPA) around the Chagos Archipelago violated UNCLOS, finding that the UK failed to consult Mauritius and respect its rights as a coastal state, including on fisheries and potential resources.

In 2019, the International Court of Justice (ICJ) issued an advisory opinion stating that the detachment of the Chagos Archipelago from Mauritius was unlawful and that the UK should end its administration “as rapidly as possible.” Though non-binding, the opinion carries authoritative weight and was endorsed by UN General Assembly Resolution 73/295.

The ITLOS Special Chamber, in a maritime delimitation case between Mauritius and the Maldives, recognised Mauritius as the coastal state over the Chagos Archipelago, rejecting UK arguments and establishing a final maritime boundary.

Collectively, these rulings form a consistent international legal consensus affirming Mauritius’s sovereignty and challenging the legitimacy of UK administration over the archipelago.

Strategic and operational considerations

Supporters of the treaty emphasised that the 99-year leaseback of Diego Garcia allows continued operation of the UK–US military base while avoiding prolonged legal disputes. Parliamentary debate noted that the agreement ensures legal certainty and continuity of military operations, while mitigating risks to airspace, communications, and maritime operations.

Donald Trump

On 20 January 2026 US President Donald Trump addressed the issue, passing heavy criticism on the UK’s controversial deal to transfer sovereignty of the Chagos Islands to Mauritius, as it includes the Naval Support Facility Diego Garcia. Trump called it an “act of great stupidity” and “total weakness” that harms national security and benefits rivals like China and Russia. Trump said the move, even with the U.K. retaining a long-term lease on Diego Garcia, undermines Western strength and used it to justify his push to acquire Greenland, though the UK government defends the agreement as ensuring the base’s future.

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