Sovereignty over the Chagos Archipelago is disputed between Mauritius and the United Kingdom. The Maldives has a separate dispute with the UK regarding the determination of the maritime boundary between the Maldives and the Chagos Archipelago. Mauritius has repeatedly stated that the Chagos Archipelago is part of its territory and that the United Kingdom (UK) claim is a violation of United Nations resolutions banning the dismemberment of colonial territories before independence. The UK government has stated that it has no doubt about its sovereignty over the Chagos, yet has also said that the Chagos will be given to Mauritius once the islands are no longer required for military purposes. Given the absence of any progress with the UK, Mauritius took up the matter at various legal and political forums. Maldives stated that, if the Chagos were re-inhabited, the Maldives claim to an extension of its Exclusive Economic Zone would be affected.
The African Union and the Non-Aligned Movement have expressed unanimous support for Mauritius on the Chagos issue.
The Constitution of Mauritius states that the Outer islands of Mauritius includes the islands of Mauritius, Rodrigues, Agaléga, Cargados Carajos and the Chagos Archipelago, including Diego Garcia and any other island comprised in the State of Mauritius. The Government of the Republic of Mauritius has stated that it does not recognise the British Indian Ocean Territory (BIOT) which the United Kingdom created by excising the Chagos Archipelago from the territory of Mauritius prior to its independence, and claims that the Chagos Archipelago including Diego Garcia forms an integral part of the territory of Mauritius under both Mauritian law and international law.
In 1965, the United Kingdom split the Chagos Archipelago away from Mauritius, and the islands of Aldabra, Farquhar, and Desroches from the Seychelles, to form the British Indian Ocean Territory. The islands were formally established as an overseas territory of the United Kingdom on 8 November 1965. However, with effect from 23 June 1976, Aldabra, Farquhar, and Desroches were returned to the Seychelles on their attaining independence.
On 18 March 2015, the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) which the United Kingdom declared around the Chagos Archipelago in April 2010 was created in violation of international law. The Prime Minister of Mauritius has stated that this is the first time that the country's conduct with regard to the Chagos Archipelago has been considered and condemned by any international court or tribunal. He described the ruling as an important milestone in the relentless struggle, at the political, diplomatic, and other levels, of successive Governments over the years for the effective exercise by Mauritius of the sovereignty it claims over the Chagos Archipelago. The tribunal considered in detail the undertakings given by the United Kingdom to the Mauritian Ministers at the Lancaster House talks in September 1965. The UK had argued that those undertakings were not binding and had no status in international law. The Tribunal firmly rejected that argument, holding that those undertakings became a binding international agreement upon the independence of Mauritius, and have bound the UK ever since. It found that the UK's commitments towards Mauritius in relation to fishing rights and oil and mineral rights in the Chagos Archipelago are legally binding.
Beginning in the late 15th century, Portuguese explorers began to venture into the Indian Ocean and recorded the location of Mauritius and the other Mascarene Islands, Rodrigues and Réunion (the latter presently a French overseas department). In the 16th century, the Portuguese were joined by Dutch and English sailors, both nations having established East India Companies to exploit the commercial opportunities of the Indian Ocean and the Far East. Although Mauritius was used as a stopping point in the long voyages to and from the Indian Ocean, no attempt was made to establish a permanent settlement.
The first permanent colony in Mauritius was established by the Dutch East India Company in 1638. The Dutch maintained a small presence on Mauritius, with a brief interruption, until 1710 at which point the Dutch East India Company abandoned the island. Following the Dutch departure, the French government took possession of Mauritius in 1715, renaming it the Île de France.
The Chagos Archipelago was known during this period, appearing on Portuguese charts as early as 1538, but remained largely untouched. France progressively claimed and surveyed the Archipelago in the mid-18th century and granted concessions for the establishment of coconut plantations, leading to permanent settlement. Throughout this period, France administered the Chagos Archipelago as a dependency of the Ile de France.
In 1810, the British captured the Ile de France and renamed it Mauritius. By the Treaty of Paris of 30 May 1814, France ceded the Ile de France and all its dependencies (including the Chagos Archipelago) to the United Kingdom.
From the date of the cession by France until 8 November 1965, when the Chagos Archipelago was detached from the colony of Mauritius, the Archipelago was administered by the United Kingdom as a Dependency of Mauritius. During this period, the economy of the Chagos Archipelago was primarily driven by the coconut plantations and the export of copra (dried coconut flesh) for the production of oil, although other activities developed as the population of the Archipelago expanded. British administration over the Chagos Archipelago was exercised by various means, including by visits to the Chagos Archipelago made by Special Commissioners and Magistrates from Mauritius.
Although the broad outlines of British Administration of the colony during this period are not in dispute, the Parties disagree as to the extent of economic activity in the Chagos Archipelago and its significance for Mauritius, and on the significance of the Archipelago’s status as a dependency. Mauritius contends that there were "close economic, cultural and social links between Mauritius and the Chagos Archipelago" and that "the administration of the Chagos Archipelago as a constituent part of Mauritius continued without interruption throughout that period of British rule". The United Kingdom, in contrast, submits that the Chagos Archipelago was only "very loosely administered from Mauritius" and "in law and in fact quite distinct from the Island of Mauritius." The United Kingdom further contends that "the islands had no economic relevance to Mauritius, other than as a supplier of coconut oil" and that, in any event, economic, social and cultural ties between the Chagos Archipelago and Mauritius during this period are irrelevant to the Archipelago’s legal status.
Beginning in 1831, the administration of the British Governor of Mauritius was supplemented by the introduction of a Council of Government, originally composed of ex-officio members and members nominated by the Governor. The composition of this Council was subsequently democratized through the progressive introduction of elected members. In 1947, the adoption of a new Constitution for Mauritius replaced the Council of Government with separate Legislative and Executive Councils. The Legislative Council was composed of the Governor as President, 19 elected members, 12 members nominated by the Governor and 3 ex-officio members.
The first election of the Legislative Council took place in 1948, and the Mauritius Labour Party (the "MLP") secured 12 of the 19 seats available for elected members.35 The MLP strengthened its position in the 1953 election by securing 14 of the available seats, although the MLP lacked an overall majority in the Legislative Council because of the presence of a number of members appointed by the Governor.
The 1953 election marked the beginning of Mauritius’ move towards independence. Following that election, Mauritian representatives began to press the British Government for universal suffrage, a ministerial system of government and greater elected representation in the Legislative Council. By 1959, the MLP-led government had openly adopted the goal of complete independence.
Constitutional Conferences were held in 1955, 1958, 1961, and 1965, resulting in a new constitution in 1958 and the creation of the post of Chief Minister in 1961 (renamed as the Premier after 1963). In 1962, Dr Seewoosagur Ramgoolam (later Sir Seewoosagur Ramgoolam) became the Chief Minister within a Council of Ministers chaired by the Governor and, following the 1963 election, formed an all-party coalition government to pursue negotiations with the British on independence.
The final Constitutional Conference was held in London in September 1965 and was principally concerned with the debate between those Mauritian political leaders favouring independence and those preferring some form of continued association with the United Kingdom. On 24 September 1965, the final day of the conference, the Secretary of State for the Colonies, the Rt. Hon. Anthony Greenwood MP, who was the minister in the United Kingdom Government with responsibility for Mauritius, announced that the United Kingdom Government intended that Mauritius would proceed to full independence.
A few weeks after the decision to detach the islands from Mauritius, the United Nations General Assembly passed Resolution 2066(XX) on 16 December 1965, which stated its belief that detaching part of a colonial territory was against customary international law as recorded earlier in Resolution 1514 of 14 December 1960. This 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." Largely because of the detachment of the islands, the International Court of Justice determined in 2019 that the decolonization of Mauritius was still not lawfully completed.
Mauritius became independent on 12 March 1968.
In conjunction with the move toward Mauritian independence, the United Kingdom formulated a proposal to separate the Chagos Archipelago from the remainder of the colony of Mauritius, and to retain the Archipelago under British control. According to Mauritius, the proposal to separate the Chagos Archipelago stemmed from a decision by the United Kingdom in the early 1960s to "accommodate the United States’ desire to use certain islands in the Indian Ocean for defence purposes."
The record before the Tribunal sets out a series of bilateral talks between the United Kingdom and the United States in 1964 at which the two States decided that, in order to execute the plans for a defence facility in the Chagos Archipelago, the United Kingdom would "provide the land, and security of tenure, by detaching islands and placing them under direct U.K. administration."
The suitability of Diego Garcia as the site of the planned defence facility was determined following a joint survey of the Chagos Archipelago and certain islands of the Seychelles in 1964. Following the survey, the United States sent its proposals to the United Kingdom, identifying Diego Garcia as its first preference as the site for the defence facility. The United Kingdom and the United States conducted further negotiations between 1964 and 1965 regarding the desirability of "detachment of the entire Chagos Archipelago," as well as the islands of Aldabra, Farquhar and Desroches (then part of the Colony of the Seychelles). They further discussed the terms of compensation that would be required "to secure the acceptance of the proposals by the local Governments."
On 19 July 1965, the Governor of Mauritius was instructed to communicate the proposal to detach the Chagos Archipelago to the Mauritius Council of Ministers and to report back on the Council’s reaction. The initial reaction of the Mauritian Ministers, conveyed by the Governor’s report of 23 July 1965, was a request for more time to consider the proposal. The report also noted that Sir Seewoosagur Ramgoolam expressed "dislike of detachment". At the next meeting of the Council on 30 July 1965, the Mauritian Ministers indicated that detachment would be "unacceptable to public opinion in Mauritius" and proposed the alternative of a long term lease, coupled with safeguards for mineral rights and a preference for Mauritius if fishing or agricultural rights were ever granted. The Parties differ in their understanding of the strength of, and motivation for, the Mauritian reaction. In any event, on 13 August 1965, the Governor of Mauritius informed the Mauritian Ministers that the United States objected to the proposal of a lease.
Discussions over the detachment of the Chagos Archipelago continued in a series of meetings between certain Mauritian political leaders, including Sir Seewoosagur Ramgoolam, and the Secretary of State for the Colonies, Anthony Greenwood, coinciding with the Constitutional Conference of September 1965 in London. Over the course of three meetings, the Mauritian leaders pressed the United Kingdom with respect to the compensation offered for Mauritian agreement to the detachment of the Archipelago, noting the involvement of the United States in the establishment of the defence facility and Mauritius’ need for continuing economic support (for example through a higher quota for Mauritius sugar imports into the United States), rather than the lump sum compensation being proposed by the United Kingdom. The United Kingdom took the firm position that obtaining concessions from the United States was not feasible; the United Kingdom did, however, increase the level of lump sum compensation on offer from £1 million to £3 million and introduced the prospect of a commitment that the Archipelago would be returned to Mauritius when no longer needed for defence purposes. The Mauritian leaders also met with the Economic Minister at the U.S. Embassy in London on the question of sugar quotas, and Sir Seewoosagur Ramgoolam met privately with Prime Minister Harold Wilson on the morning of 23 September 1965. The United Kingdom’s record of this conversation records Prime Minister Wilson having told Sir Seewoosagur Ramgoolam that
in theory, there were a number of possibilities. The Premier and his colleagues could return to Mauritius either with Independence or without it. On the Defence point, Diego Garcia could either be detached by order in Council or with the agreement of the Premier and his colleagues. The best solution of all might be Independence and detachment by agreement, although he could not of course commit the Colonial Secretary at this point.
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:
Summing up the discussion, the SECRETARY OF STATE asked whether he could inform his colleagues that Dr. Seewoosagur Ramgoolam, Mr. Bissoondoyal and Mr. Mohamed were prepared to agree to the detachment of the Chagos Archipelago on the understanding that he would recommend to his colleagues 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. Sir Seewoosagur Ramgoolam’s note provided as follows:
Dear Mr. Trafford Smith,
I and Mr Mohamed have gone through the enclosed paper on the question of Diego Garcia and another near island (i.e. two altogether) and we wish to point out the amendments that should be effected on page 4 of this document. The matters to be added formed part of the original requirements submitted to H.M.G. We think that these can be incorporated in any final agreement.
With kind regards, S. Ramgoolam P.S. The two copies handed over to me are herewith enclosed.
The third page to Sir Seewoosagur Ramgoolam’s note set out the following items:
- (vii) Navigational & Meteorological facilities
- (viii) Fishing rights
- (ix) Use of Air Strip for Emergency Landing and if required for development of the other islands
- (x) Any mineral or oil discovered on or near islands to revert to the Mauritius Government.
These additions were incorporated into paragraph 22 of the final record of the Lancaster House Meeting, which the Tribunal considers to warrant quotation in full:
RECORD OF A MEETING HELD IN LANCASTER HOUSE AT 2. 30 P.M. ON THURSDAY 23rd SEPTEMBER
MAURITIUS DEFENCE MATTERS
Present:- The Secretary of State (in the Chair) Lord Taylor Sir Hilton Poynton Sir John Rennie Mr. P. R. Noakes Mr. J. Stacpoole Sir S. Ramgoolam Mr. S. Bissoondoyal Mr. J. M. Paturau Mr. A. R. Mohamed
THE SECRETARY OF STATE expressed his apologies for the unavoidable postponements and delays which some delegations at the Constitutional Conference had met with earlier in the day. He explained that he was required to inform his colleagues of the outcome of his talks with Mauritian Ministers about the detachment of the Chagos Archipelago at 4 p.m. that afternoon and was therefore anxious that a decision should be reached at the present meeting.
2. He expressed his anxiety that Mauritius should agree to the establishment of the proposed facilities, which besides their usefulness for the defence of the free world, would be valuable to Mauritius itself by ensuring a British presence in the area. On the other hand it appeared that the Chagos site was not indispensable and there was therefore a risk that Mauritius might lose this opportunity. In the previous discussions he had found himself caught between two fires: the demands which the Mauritius Government had made, mainly for economic concessions by the United States, and the evidence that the United States was unable to concede these demands. He had throughout done his best to ensure that whatever arrangements were agreed upon should secure the maximum benefit for Mauritius. He was prepared to recommend to his colleagues if Mauritius agreed to the detachment of the Chagos Archipelago:-
- (i) negotiations for a defence agreement between Britain and Mauritius;
- (ii) that if Mauritius became independent, there should be an understanding that the two governments would consult together in the event of a difficult internal security situation arising in Mauritius;
- (iii) that the British Government should use its good offices with the United States Government in support of Mauritius request for concessions over the supply of wheat and other commodities
- (iv) that compensation totalling up to £3m. should be paid to the Mauritius Government over and above direct compensation to landowners and others affected in the Chagos Islands.
This was the furthest the British Government could go. They were anxious to settle this matter by agreement but the other British Ministers concerned were of course aware that the islands were distant from Mauritius, that the link with Mauritius was an accidental one and that it would be possible for the British Government to detach them from Mauritius by Order in Council.
3. SIR S. RAMGOOLAM replied that the Mauritius Government were anxious to help and to play their part in guaranteeing the defence of the free world. He asked whether the Archipelago could not be leased, (THE SECRETARY OF STATE said that this was not acceptable). MR. BISSOONDOYAL enquired whether the Islands would revert to Mauritius if the need for defence facilities there disappeared. THE SECRETARY OF STATE said that he was prepared to recommend this to his colleagues.
4. MR. PATURAU said that he recognised the value and importance of an Anglo-Mauritius defence agreement, and the advantage for Mauritius if the facilities were established in the Chagos Islands, but he considered the proposed concessions a poor bargain for Mauritius.
5. MR. BISSOONDOYAL asked whether there could be an assurance that supplies and manpower from Mauritius would be used so far as possible. THE SECRETARY OF STATE said that the United States Government would be responsible for construction work and their normal practice was to use American manpower but he felt sure the British Government would do their best to persuade the American Government to use labour and materials from Mauritius.
6. SIR S. RAMGOOLAM asked the reason for Mr. Koenig’s absence from the meeting and MR. BISSOONDOYAL asked whether the reason was a political one, saying that if so this might affect the position.
7. Mr. MOHAMED made an energetic protest against repeated postponements of the Secretary of State's proposed meeting with the M.C.A. [Muslim Committee of Action], which he regarded as a slight to his party.
8. THE SECRETARY OF STATE repeated the apology with which he had opened the meeting, explaining that it was often necessary in such conferences to concentrate attention on a delegation which was experiencing acute difficulties, while he himself had been obliged to devote much time to a crisis in another part of the world.
9. MR MOHAMED then handed the Secretary of State a recent private letter from Mauritius which disclosed that extensive misrepresentations about the course of the Conference had been published in a Parti Mauricien newspaper. THE SECRETARY OF STATE commented that such misrepresentations should be disregarded, and that MR. MOHAMED had put forward the case for his community with great skill and patience.
10. MR. MOHAMED said that his party was ready to leave the bases question to the discretion of H.M.G. and to accept anything which was for the good of Mauritius. Mauritius needed a guarantee that defence help would be available nearby in case of need.
11. At SIR S. RAMGOOLAM’s request the Secretary of State repeated the outline he had given at a previous meeting of the development aid which would be available to Mauritius between 1966–1968, viz. a C.D. & W. [Commonwealth Development & Welfare] allocation totalling £2.4 million (including carryover) thus meaning that £800,000 a year would be available by way of grants in addition Mauritius would have access to Exchequer loans, which might be expected to be of the order of £1m. a year, on the conditions previously explained. He pointed out that Diego Garcia was not an economic asset to Mauritius and that the proposed compensation of £3m. would be an important contribution to Mauritius development. There was no chance of raising this figure.
12. SIR S. RAMGOOLAM said that there was a gap of some £4m. per year between the development expenditure which his government considered necessary in order to enable the Mauritian economy to "take off" and the resources in sight, and enquired whether it was possible to provide them with additional assistance over a 10 year period to bridge this gap.
13. THE SECRETARY OF STATE mentioned the possibility of arranging for say £2m. of the proposed compensation to be paid in 10 instalments annually of £200,000.
14. SIR S. RAMGOOLAM enquired about the economic settlement with Malta on independence and was informed that these arrangements had been negotiated in the context of a special situation for which there was no parallel in Mauritius.
15. SIR H. POYNTON pointed out that if Mauritius did not become independent within three years, the Colonial Office would normally consider making a supplementary allocation of C.D. & W. grant money to cover the remainder of the life of the current C.D. & W. Act, i.e. the period up to 1970. He added that if Mauritius became independent, they would normally receive the unspent balance of their C.D. & W. allocation in a different form and it would be open to them after the three year period to seek further assistance such as Britain was providing for a number of independent Commonwealth countries.
16. SIR S. RAMGOOLAM said that he was prepared to agree in principle to be helpful over the proposals which H.M.G. had put forward but he remained concerned about the availability of capital for development in Mauritius and hoped that the British Government would be able to help him in this respect.
17. MR. BISSOONDOYAL said that while it would have been easier to reach conclusions if it had been possible to obtain unanimity among the party leaders, his party was prepared to support the stand which the Premier was taking. They attached great importance to British assistance being available in the event of a serious emergency in Mauritius.
18. MR. PATURAU asked that his disagreement should be noted. The sum offered as compensation was too small and would provide only temporary help for Mauritius economic needs. Sums as large as £25m. had been mentioned in the British press and Mauritius needed a substantial contribution to close the gap of £4-5m. in the development budget. He added that since the decision was not unamimous [sic], he foresaw serious political trouble over it in Mauritius.
19. THE SECRETARY OF STATE referred to his earlier suggestion that payment of the monetary compensation should be spread over a period of years.
20. SIR S. RAMGOOLAM said that he was hoping to come to London for economic discussions in October. The Mauritius Government’s proposals for development expenditure had not yet been finalised, but it was already clear that there would be a very substantial gap on the revenue side.
21. SIR H. POYNTON said that the total sum available for C.D. & W. assistance to the dependent territories was a fixed one and it would not be possible to increase the allocation for one territory without proportionately reducing that of another.
22. Summing up the discussion, the SECRETARY OF STATE asked whether he could inform his colleagues that Dr. [Sir Seewoosagur] Ramgoolam, Mr. Bissoondoyal and Mr. Mohamed were prepared to agree to the detachment of the Chagos Archipelago on the understanding that he would recommend to his colleagues 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 £3m. should be paid to the Mauritius Government over and above direct compensation to landowners and the cost of resettling others affected in the Chagos Islands; (iv) the British Government would use their 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) the British Government would use their good offices with the U.S. Government to ensure that the following facilities in the Chagos Archipelago would remain available to the Mauritius Government as far as practicable: (a) Navigational and Meteorological facilities; (b) Fishing Rights; (c) Use of Air Strip for emergency landing and for refuelling civil planes without disembarkation of passengers. (vii) that if the need for the facilities on the islands disappeared the islands should be returned to Mauritius; (viii) that the benefit of any minerals or oil discovered in or near the Chagos Archipelago should revert to the Mauritius Government.
23. SIR S. 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.
24. THE SECRETARY OF STATE pointed out that he had to leave almost immediately to convey the decision to his own colleagues and LORD TAYLOR urged the Mauritian Ministers not to risk losing the substantial sum offered and the important assurance of a friendly military presence nearby.
25. SIR S. RAMGOOLAM said that Mr. Paturau had urged him to make a further effort to secure a larger sum by way of compensation, but the Secretary of State said there was no hope of this.
26. SIR J. RENNIE said that while he had hoped that Mauritius would be able to obtain trading concessions in these negotiations, this was now ruled out. It was in the interest of Mauritius to take the opportunity offered to ensure a friendly military presence in the area. What was important about the compensation was the use to which the lump sum was put.
27. SIR S. RAMGOOLAM mentioned particular development projects, such as a dam and a land settlement scheme, and expressed the hope that Britain would make additional help available in an independence settlement.
28. SIR H. POYNTON said that the Mauritius Government should not lose sight of the possibility of securing aid for such purposes from the World Bank, the I.D.A. and from friendly governments. While Mauritius remained a colony such powers as Western Germany regarded Mauritius economic problems as a British responsibility but there was the hope that after independence aid would be available from these sources. When Sir S. Ramgoolam suggested that he had said that grants could be extended for up to 10 years, Sir H. Poynton pointed out that he had only indicated that when the period for which the next allocation had been made expired, it would be open to the Mauritius Government to seek further assistance, from Britain, even though Mauritius had meanwhile become independent. It would not be possible to reach any understanding at present beyond saying that independence did not preclude the possibility of negotiating an extension of Commonwealth aid.
29. At this point the SECRETARY OF STATE left for 10, Dowing Street [sic], after receiving authority from Sir S. Ramgoolam and Mr. Bissoondoyal to report their acceptance in principle of the proposals outlined above subject to the subsequent negotiation of details. Mr. Mohamed gave the same assurance, saying that he spoke also for his colleague Mr. Osman. Mr. Paturau said he was unable to concur.
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 -
5. 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.
6. 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:
As already stated in paragraph 6 of my despatch No. 423, the Chagos Archipelago will remain under British sovereignty. The islands are required for defence facilities and there is no intention of permitting prospecting for minerals or oils on or near them. The points set out in your paragraph 1 should not therefore arise but I shall nevertheless give them further consideration in view of your request.
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;
1. 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.
4. 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.
Main article: Depopulation of Chagossians from the Chagos Archipelago
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 right of return.
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 fully protected 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.
On 1 December 2010, WikiLeaks release a leaked US Embassy London diplomatic cable dating back to 2009  which exposed British and US calculations 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].
The cable (reference ID "09LONDON1156" ) was classified as confidential and "no foreigners", and leaked as part of the Cablegate cache.
In March 2014, it was reported that the UK government were sending experts to the islands to examine "options and risks" of resettlement.
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.
On 18 March 2015, the Permanent Court of Arbitration ruled that the Chagos Marine Protected Area was illegal.
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 its 25 February 2019 ruling, the Court deemed the United Kingdom's separation of the Chagos Islands from the rest of Mauritius in 1965, when both were colonial territories, to be unlawful and found that the United Kingdom is obliged to end "its administration of the Chagos Islands as rapidly as possible."
On 28 January 2021, the United Nation's International Tribunal for the Law of the Sea ruled, in a dispute between Mauritius and Maldives on their maritime boundary, that the United Kingdom has no sovereignty over the Chagos Archipelago, and that Mauritius is sovereign there. The United Kingdom disputes and does not recognise the tribunal's decision.