A Bill to give effect to, and make provision in connection with, an agreement between the governments of the United Kingdom and the Republic of Mauritius concerning the Chagos Archipelago.
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Page 1
Source Bill 285 EN 2024-25
1. This clause sets out when the main provisions in the Bill come into force. Clauses 2 to 4, which deal with dissolution of BIOT, the continued administration of Diego Garcia, and citizenship of persons connected to the Chagos Archipelago, will come into force when the Treaty comes into force.
2. Entry into force of the Treaty is defined in Article 18 of the Treaty, as being the first day of the first month following the date of receipt of the later note by which Mauritius and the UK notify each other that they have completed their respective internal requirements and procedures necessary.
3. Under subsection (4), the Secretary of State will publish in the London Gazette notice of when the Treaty, and therefore clauses 2, 3 and 4, comes into force.
4. Clause 6 (described below) deals with the commencement of the other clauses in the Bill.
Source Bill 285 EN 2024-25
5. This clause provides for the dissolution of BIOT. It brings to an end His Majesty's sovereignty over the area which currently comprises BIOT. This addresses Article 1 of the Treaty, which states that the Parties agree that Mauritius is sovereign over the Chagos Archipelago, including Diego Garcia.
6. Subsection (2)(a) revokes the British Indian Ocean Territory (Constitution) Order 2004, which currently provides the constitution of BIOT.
7. As BIOT will no longer exist as a British overseas territory, susbection 2(2)(b) removes reference to BIOT from Schedule 6 to the British Nationality Act 1981. The Interpretation Act 1978 defines the term "British overseas territory" across the statute-book by reference to that Schedule.
Source Bill 285 EN 2024-25
8. This clause provides for the continued administration of Diego Garcia by the United Kingdom, in accordance with the Treaty and its provisions on UK jurisdiction and control, through a partial saving of existing law. Changes to the law will be needed to reflect the new status of Diego Garcia (including to ensure that the law respects the limitations in the Treaty). Through this clause, the Bill establishes a default position of continuity in the law of and relating to Diego Garcia, to avoid legal gaps on entry into force of the Treaty. Necessary changes to the law will then be made under the prerogative, the powers conferred by clause 5, or other existing statutory powers in the relevant jurisdictions.
9. Subsection (1) and (2) set out a general saving, preserving all laws of or relating to BIOT as laws of or relating to Diego Garcia.
10. Subsection (2) applies to any legislation or rule of law of England, Wales, Scotland, Northern Ireland and any of the Crown Dependencies or the Overseas Territories which currently relates to BIOT.
11. His Majesty in Council has "plenary", i.e. full, power to legislate for BIOT. Subsection (3) clarifies that the effect of subsections (1) and (2) is to preserve that power as a prerogative power to legislate for Diego Garcia.
12. Subsection (4)(a) relates to Schedule 6 to the British Nationality Act 1981 ("the 1981 Act") which lists the British overseas territories. As noted above, the definition of "British overseas territory" provided by the Interpretation Act 1978 is by reference to the 1981 Act. While clause 2(2)(b) removes BIOT from this list, the purpose of subsection(4)(a) is to clarify that, where a law currently extends to BIOT because BIOT is an overseas territory listed in Schedule 6 to the 1981 Act, subsection (1) still preserves this law as a law of Diego Garcia. Similarly, where a law relates to BIOT because BIOT is an overseas territory listed in Schedule 6, subsection (2) preserves this as a law relating to Diego Garcia, even though Diego Garcia will not be listed as an overseas territory.
13. Subsection (4)(b) has the effect that laws saved by subsection (1) or (2) can be amended at or after commencement in the usual way, notwithstanding that saving.
14. Subsection (5) provides that, despite the revocation of the BIOT (Constitution) Order 2004, any legislation made under that Order will continue to have effect by virtue of the saving provision in susbection(1). This includes legislation made by the Commissioner for BIOT under section 3 of that Order, which is therefore preserved as the law of Diego Garcia.
15. Subsection (6) provides that, throughout the whole Bill, the term "Diego Garcia" includes the whole area for which the UK can legislate under the Treaty. See in particular Article 19 and Annex 2 of the Treaty in this respect.
Page 2
Source Bill 285 EN 2024-25
16. This clause makes provision about British nationality, specifically about the entitlement to British and British overseas territory citizenship of persons who were born in BIOT and their descendants ("Chagossians").
17. British Overseas Territories citizenship ("BOTC") is a form of British nationality held through a close and continuing connection with a British overseas territory. A British overseas territories citizen can hold a British passport and get consular assistance and protection from UK diplomatic posts. The difference between British citizenship and BOTC is the right of abode in the UK. All British citizens have the right of abode within the UK, meaning they are completely free from immigration control and can live and work in the UK permanently, without needing to seek official permission from the Home Office. However, BOTC does not directly provide the right of abode.
18. The Bill will not affect either British citizenship or BOTC acquired before commencement, nor will it affect current routes to British citizenship, with their existing expiry dates. However, after BIOT ceases to be a British overseas territory, no-one will be entitled to acquire BOTC on the basis of a connection to BIOT or the Chagos Archipelago.
19. Section 17H currently entitles a person to BOTC if they are the direct descendant of a person who was a citizen of the UK and Colonies because they were born in BIOT (or were born before 1965 on the islands which subsequently became BIOT). This entitlement applies only to individuals who have never previously held BOTC or a British Dependent Territories citizenship, and is time limited: applications must be made within a certain period from the date on which section 17H came into force, which was 23 November 2022.
20. Under section 4K of the 1981 Act, a person who is entitled to hold BOTC under section 17H is entitled to be registered as a British citizen (subject to the exceptions set out in the 1981 Act).
21. Subsections (4), (5) and (6) amend the 1981 Act by inserting new sections 4KA and 25A, and omitting section 17H, of that Act.
22. The omission of section 17H, combined with the new section 25A, means that after the commencement of this clause, a person will no longer be entitled to claim BOTC on the basis of descent from a person born on the Chagos Archipelago.
23. The new section 4KA of the 1981 Act will provide that a Chagossian who was previously eligible for British citizenship by virtue of section 17H of the 1981 Act in combination with section 4K of that Act ("the s. 17H route") will be eligible to claim such citizenship until the original expiry of the s. 17H route, as applicable to them. This means, for example, that after clause 4 commences, a person who was 18 or over on 23 November 2022, who wishes to apply for British citizenship under section 4KA, must do so before 23 November 2027.
24. Any Chagossians who are born between the date of entry into force of the Treaty and the expiry of the s17H route who would have been eligible for that route continue to be eligible to apply for British citizenship (but not BOTC).
25. Subsection (8) creates a transitional provision in relation to applications for British citizenship or BOTC which have been made before the day on which commencement of this clause occurs, but have not been determined at that point. These applications will be dealt with on the basis of section 17H and section 4K as they applied before commencement of this clause.
26. Subsection (9) provides that British citizenship and BOTC acquired before the entry into force of the Treaty are not affected by anything in the Bill.
27. Clause 4(2) makes it clear that, in recognition of the changes made by the remainder of the clause, the general continuity proposition in clause 3(2) does not apply to the 1981 Act itself. It will, however, apply to other legislation that currently applies to BIOT by virtue of its inclusion in the list of British overseas territories in Schedule 6 to the 1981 Act (as explained in relation to clause 3(4)(a)).
Page 3
Source Bill 285 EN 2024-25
28. Clause 5 confers a power to implement the Treaty and make provision resulting from it in domestic law.
29. Subsection (1) gives His Majesty the power to make an Order in Council making any provision which he considers appropriate as a result of the Treaty. This might include, for example, provision directly implementing the Treaty, or provision which needs to be made as a result of the Treaty, to reflect the fact that BIOT no longer exists as an overseas territory. Orders in Council under clause 5(1) may also make consequential, supplementary, transitional etc. provision.
30. This power includes (under subsection (2)) a power to amend, repeal or revoke any existing legislation of any part of the United Kingdom, the Crown Dependencies or the Overseas Territories. Orders in Council under clause 5 may amend legislation which forms part of the law of Diego Garcia pursuant to the general saving made by clause 3.
31. The Parliamentary procedures applying to Orders in Council made using this power will depend on their content. Orders in Council under Clause 5 are not subject to any Parliamentary procedure, unless they amend, repeal or revoke any Act of Parliament or provision made under an Act of Parliament by statutory instrument, in which case they will be subject to the negative procedure.
32. Subsection (4) and (6) together provide that the statutory power conferred by clause 5 does not limit any of His Majesty's powers under his prerogative. This includes the prerogative power to legislate for Diego Garcia which is preserved by virtue of clause 3. Subsection (5) explains how the use of those powers after entry into force of the Treaty is to be treated under the Foreign Jurisdiction Act 1890 and the Statutory Instruments Act 1946. Part of the intention is to maintain a clear distinction between prerogative and statutory orders, notwithstanding the fact that the Bill clarifies or confirms certain aspects of the prerogative as forming part of the new legal framework for Diego Garcia.
33. Subsection (6) makes it clear that His Majesty's prerogative power to legislate for British Indian Ocean Territory may be used after this clause has come into force, to make laws which take effect at or after entry into force of the Treaty, which will be saved as laws of Diego Garcia. This is to avoid any doubt as to the ability under the prerogative to legislate in a way that anticipates the new status of Diego Garcia and can take effect together with the change in status.
Page 4
Source Bill 285 EN 2024-25
34. Clause 6 makes provision for clause 4 of the Bill to come into force on the day which the Bill is passed.
35. Subsection (2) is self-explanatory.
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
Clause 1, page 1, line 7, leave out subsection (2) and insert—
“(1A) The Treaty and sections 2 to 4 of this Act do not come into force until the duties outlined in section [The additional period and right to extend: duty to publish legal advice and risk assessments] are discharged.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025Member's explanatory statement
This amendment together with NC2 would prevent the Treaty from coming into force until the Government has published any legal advice or risk assessments regarding the UK’s ability to extend its rights over Diego Garcia after the initial period specified in the Treaty.
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
Clause 5, page 3, line 29, leave out subsections (1) to (4)
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
Clause 5, page 3, line 36, at beginning insert “With the exception of the subject matters listed in subsection (3A),”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
Clause 5, page 4, line 3, at end insert—
“(3A) An order under this section relating to Diego Garcia, or the rights of Chagossians residing in the United Kingdom, may not be made unless a draft of the order has been laid before Parliament and approved by a resolution of each House.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
Clause 5, page, 3, line 40, leave out “is subject to annulment in pursuance of a resolution of either House of Parliament” and insert “may not be made unless a draft of the order has been laid before Parliament and approved by a resolution of each House.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
Clause 6, page 4, line 17, leave out "see section 1(2)" and insert "see section 1(1A)"
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025Member's explanatory statement
This amendment is consequential on NC2
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
To move the following Clause—
“Approval of payments to Mauritius by the House of Commons
(1) No payment may be made by the Government of the United Kingdom to the Government of Mauritius under Article 11 (1)(a) of the Treaty without the approval of the House of Commons.
(2) No development framework under Article 11 (1)(c) may be agreed by the Government of the United Kingdom with the Government of Mauritius without the approval of the House of Commons.
(3) No payment may be made under any development framework agreed between the Government of the United Kingdom and the Government of Mauritius without the approval of the House of Commons.
(4) The approval required by subsections (1), (2) and (3) must be in the form of a resolution of the House of Commons.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025Member's explanatory statement
This new clause requires parliamentary approval for any payment by the UK Government to the Government of Mauritius under the Treaty.
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
To move the following Clause—
“The additional period and right to extend: duty to publish legal advice and risk assessments
(1) Within six months of this Act receiving Royal Assent, the Secretary of State must lay before both Houses of Parliament any legal advice and any risk assessments given to the Government relating to—
(a) the ability of the United Kingdom to extend the duration of the Treaty’s provisions for the additional period of 40 years (“the additional period”) specified in Article 13(2) of the Treaty, including—
(i) any advice pertaining to the automaticity, or otherwise, of the UK securing the additional period;
(ii) any obligations placed on both parties to negotiate the additional period;
(iii) any risk assessment of the impact on the United Kingdom’s strategic interests of not securing the additional period; and
(b) the ‘right of first refusal’ offered to the United Kingdom should the additional period not be negotiated at the end of the Treaty’s initial duration under Article 13(5) of the Treaty, including whether such a right exists if the additional period expires without a further extension being agreed.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
To move the following Clause—
“Written instrument on the Marine Protected Area: approval by the House of Commons
(1) No written instrument on the establishment and management of its Marine Protected Area in the Chagos Archipelago provided for by Article 5 of the Treaty, including any changes to current restrictions on fishing, commercial and extractive activities, may be agreed to by the Government of the United Kingdom unless—
(a) a Minister of the Crown has laid before Parliament a copy of the written instrument,
(b) the written instrument and an explanatory memorandum has been published, and
(c) period A has expired without the House of Commons having resolved, within period A, that the written instrument should not be agreed.
(2) Period A is the period of 21 sitting days beginning with the first sitting day after the date on which the requirement in subsection (1)(a) is met.
(3) “An explanatory memorandum” has the meaning given in section 24 of the Constitutional Reform and Governance Act 2010.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025Member's explanatory statement
This new clause provides that any written instrument on the Marine Protected Area will be subject to the approval of the House of Commons in a process equivalent to that required for treaties under section 20 of the Constitutional Reform and Governance Act 2010.
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
To move the following Clause—
“Ecological status of the Marine Protected Area
(1) The Secretary of State must, within two years of the passing of this Act and within every subsequent two years, lay before both Houses of Parliament and publish a report on the status of the Marine Protected Area (the “MPA”).
(2) Any report made under subsection (1) must include, but not be limited to—
(a) numbers of different species of coral, fish and molluscs in the Marine Protected Area;
(b) coral reef resilience;
(c) fish stocks;
(d) ocean acidification;
(e) any degradation of the marine or terrestrial environments; and
(f) a complete record of the vessels (nature and flag) that enter the MPA.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025Member's explanatory statement
This new clause requires the Secretary of State to report regularly on the status of the Marine Protected Area.
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
To move the following Clause—
“Reports to the Intelligence and Security Committee
(1) The Secretary of State must, within twelve months of this Act receiving Royal Assent, and every year subsequently, report to the Intelligence and Security Committee of Parliament, established under section 1 of the Justice and Security Act 2013, on the security of the military base on Diego Garcia and the buffer zone.
(2) The report in subsection (1) must include, but shall not be limited to—
(a) the security of the buffer zone;
(b) the management and use of the electromagnetic spectrum;
(c) the presence of any foreign security forces on the islands, whether civilian or military;
(d) a complete record of the vessels, including their nature and flag, that enter the Marine Protected Area;
(e) a complete record of the notifications the United Kingdom has given the Government of Mauritius about activity on Diego Garcia;
(f) a complete record of any information passed from the United Kingdom to the Government of Mauritius, including any military operations, personnel movements, infrastructure development, communications, and logistical support.
(3) For the purposes of this section, “buffer zone” has the meaning of the 24 nautical miles surrounding the island of Diego Garcia.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025Member's explanatory statement
This new clause requires the Secretary of State to report annually to the Intelligence and Security Committee about the security of the military base on Diego Garcia and the security of the buffer zone.
Tabled: 10 Oct 2025
Notice of Amendments as at 10 October 2025
NO DECISION has been made on this amendment
To move the following Clause—
“Report on the impact of UNCLOS on the operation of the Treaty
(1) The Secretary of State must report to Parliament within one year of the passing of this Act, and each subsequent year, on the impact that the United Nations Convention on the Law of the Sea (‘UNCLOS’) has had on the operation of the Treaty.”
Type: Opposition
Signatures: 1
Priti Patel (Con - Witham) - 10 Oct 2025Member's explanatory statement
This new clause requires the Secretary of State to report to Parliament annually about the impact that the United Nations Conventions on the Law of the Sea has on the operation of the Treaty.