[] CONTENTS 1Commencement of Treaty and main provisions of this Act 2Referendum 3Dissolution of the British Indian Ocean Territory 4Continued administration of Diego Garcia 5Citizenship of persons connected with the Territory 6Further provision: Orders in Council 7Cost of the Treaty 8Parliamentary oversight and approval of expenditure 9Commencement and short title []

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.

Be it enacted by the King’s most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the authority of the same, as follows:—
1 Commencement of Treaty and main provisions of this Act (1)

In this Act, “the Treaty” means the agreement entitled “Agreement between the Government of the United Kingdom of Great Britain and Northern Ireland and the Government of the Republic of Mauritius concerning the Chagos Archipelago including Diego Garcia” that was signed at London and Port Louis on 22 May 2025.

 (2)

When the Treaty comes into force, so do sections 3 to 5, subject to subsections (3) and (4).

 (3)

Sections 3 to 5 of this Act come into force only when the Secretary of State has sought to negotiate an amendment to Article 11 of the Treaty to ensure that the United Kingdom would cease to make payments to the government of Mauritius in the event that the use of the Base for military purposes became impossible.

 (4)

Sections 3 to 5 of this Act come into force only when the conditions in section 2 have been met.

 (5)

The time at which that happens is referred to in this Act as “commencement”.

 (6)

The Secretary of State must publish in the London Gazette notice of that time.
2 Referendum (1)

Subsections (2) to (6) are the conditions of this section for the purposes of section 1(4).

 (2)

Within six months of the day on which this Act is passed, the Secretary of State must conduct a referendum of the Chagossian community.

 (3)

The referendum must be conducted in writing and in a format and language as considered appropriate by the Secretary of State to be satisfied the response will be valid.

 (4)

The question to be put to the Chagossian community in the referendum is stated in subsection (5).

 (5)

The question is—

In recognising the international principles of self-determination, do you agree that the implementation of the Treaty agreed between the United Kingdom and Mauritius must guarantee the rights of Chagossians in a legal right—

 (a)

of resettlement on the Islands of the Chagos Archipelago other than Diego Garcia,

 (b)

of participation in the operation in and opportunities of working in and visiting Diego Garcia, and

 (c)

to be involved in decision making on the operation of the Trust Fund for the benefit of the Chagossian Community?

(6)

Within 30 days of the result of the referendum the Secretary of State must lay a statement before both Houses of Parliament setting out how they intend to respond to the referendum.

 (7)

In this section, “Chagossian community” means those Chagossians identified by the Secretary of State who will be impacted by the Act.
3 Dissolution of the British Indian Ocean Territory (1)

His Majesty is no longer sovereign over the area comprising the British Indian Ocean Territory immediately before commencement, and no longer has jurisdiction over that area except in relation to Diego Garcia (see section 4).

 (2)

Accordingly—

 (a)

the British Indian Ocean Territory (Constitution) Order 2004 is revoked, and

 (b)

in Schedule 6 to the British Nationality Act 1981 (list of British overseas territories for the purposes of that Act and the Interpretation Act 1978), the entry for the British Indian Ocean Territory is repealed.
4 Continued administration of Diego Garcia (1)

The law of the British Indian Ocean Territory immediately before commencement continues as the law of Diego Garcia.

 (2)

Any legislation or rule of law of any of His Majesty’s dominions that related to the British Indian Ocean Territory immediately before commencement relates in the same way to Diego Garcia.

 (3)

It follows, in particular, that His Majesty has under his prerogative the like powers to make laws for Diego Garcia as His Majesty had before commencement for the British Indian Ocean Territory.

 (4)

Subsections (1) and (2)—

 (a)

are not limited by the repeal made by section 3(2)(b) (but see section 5(2));

 (b)

are subject to any other change in the law taking effect at or after commencement (and do not limit any power to make such changes).

 (5)

The revocation made by section 3(2)(a) does not affect the continuation under subsection (1) of legislation made under the revoked Order.

 (6)

In this Act, “Diego Garcia” includes the whole area over which the United Kingdom is entitled to exercise jurisdiction by virtue of Articles 2 and 9 of the Treaty.
5 Citizenship of persons connected with the Territory (1)

In this section, the 1981 Act means the British Nationality Act 1981.

 (2)

Section 4(2) does not apply to the 1981 Act or any instrument made under it (but this subsection does not affect any other legislation drawing meaning from Schedule 6 to the 1981 Act or amended by Schedule 7 to that Act).

 (3)

The 1981 Act is amended as set out in subsections (4) to (6).

 (4)

After section 4K insert—

4KA Acquisition by registration: persons connected with the former British Indian Ocean Territory (1)

A person is entitled to be registered as a British citizen on an application made under this section if—

 (a)

they were born before 23 November 2027,

 (b)

they are a direct descendant of a person (“P”) who was a citizen of the United Kingdom and Colonies by virtue of P’s birth in the former British Indian Ocean Territory or, prior to 8 November 1965, in the islands designated as the British Indian Ocean Territory on that date, and

 (c)

they have never been a British citizen.

 (2)

An application under this section must be made—

 (a)

in the case of a person born before 23 November 2004, before 23 November 2027;

 (b)

in the case of a person born on or after 23 November 2004, before the day on which the person reaches the age of 23 years.

(5)

Omit section 17H (entitlement to registration as British overseas territories citizen for descendants of certain persons born in the British Indian Ocean Territory).

 (6)

After section 25 insert—

25A Limitation in respect of the British Indian Ocean Territory

Notwithstanding anything else in this Part, no person may become a British overseas territories citizen by descent by virtue of the British overseas territories citizenship of a parent if—

 (a)

the parent’s citizenship was acquired by virtue of a connection with the British Indian Ocean Territory, and

 (b)

at the time of the person’s birth, the parent would not, absent that connection, have had or been entitled to acquire British overseas territories citizenship by virtue of a connection with any other territory.

(7)

In consequence of the repeal made by subsection (5)—

 (a)

in section 4K(1)(a) of the 1981 Act (entitlements giving rise to entitlement to registration under that section), for “17F or 17H” substitute “or 17F”;

 (b)

in the Nationality and Borders Act 2022, omit section 3 (insertion of section 17H of the 1981 Act).

 (8)

The repeals made by subsections (5) and (7) do not apply in relation to an application under section 4K or 17H of the 1981 Act made (but not determined) before the day on which commencement falls; and nothing in this Act affects the determination of such an application.

 (9)

Nothing in this Act affects a person’s British citizenship or British overseas territories citizenship acquired before commencement.

 (10)

This section has the same extent as Part 1 of the 1981 Act.
6 Further provision: Orders in Council (1)

His Majesty may by Order in Council—

 (a)

make any provision that appears to His Majesty to be appropriate as a result of the Treaty, and

 (b)

make consequential, supplementary, incidental, transitional or saving provision in relation to—

 (i)

this Act, or

 (ii)

an Order under paragraph (a).

 (2)

An Order under this section may amend, repeal or revoke any legislation of any of His Majesty’s dominions passed or made before commencement (including legislation forming part of the law of Diego Garcia by virtue of section 4(1)).

 (3)

An Order under this section is subject to annulment in pursuance of a resolution of either House of Parliament if it amends, repeals or revokes—

 (a)

an Act, or

 (b)

provision made under an Act by statutory instrument, other than an earlier Order under this section.

 (4)

This section does not limit the prerogative powers.

 (5)

The prerogative powers to make laws for the British Indian Ocean Territory before commencement may be exercised to make provision intended to take effect at or after commencement as provision continued under 4(1).

 (6)

The exercise of the prerogative powers after commencement is not, as a result of any provision of this Act or the Treaty, to be regarded—

 (a)

for the purposes of the Foreign Jurisdiction Act 1890 (the 1890 Act), as the exercise of powers in pursuance of that Act, or

 (b)

for the purposes of section 1(1) of the Statutory Instruments Act 1946, as the exercise of powers conferred by this Act or the 1890 Act.

 (7)

In this section, “the prerogative powers” means His Majesty’s powers under his prerogative.
7 Cost of the Treaty

The Secretary of State must publish a statement setting out—

 (a)

the total real terms cost of payments to be made to Mauritius under the Treaty;

 (b)

the full methodology and justification of the discount mechanism used to calculate the total cost;

 (c)

the methodology used to calculate the total cost of the Treaty by—

 (i)

the Office for Budget Responsibility,

 (ii)

the Government Actuary’s Department, and

 (iii)

the Treasury.
8 Parliamentary oversight and approval of expenditure (1)

The Secretary of State must, within the first financial year following the day on which this Act is passed, lay before the House of Commons, for its approval, an estimate of the expenditure that is anticipated to be incurred by the Government of the United Kingdom in connection with the commitments made under the terms of the Treaty, including, but not limited to—

 (a)

any payments made or to be made, or financial commitments entered into, with the government of the Republic of Mauritius in accordance with the Treaty; and

 (b)

the costs associated with the continued administration, maintenance, and operation of Diego Garcia.

 (2)

In each fifth successive financial year after the first financial year as set out above, the Secretary of State must lay an estimate in accordance with subsection (1).

 (3)

If the payments incurred by the Government of the United Kingdom are greater than those anticipated in the estimate specified in subsection (1) or (2), the Secretary of State must lay before the House of Commons, for its approval, a supplementary estimate.

 (4)

If at any stage during the operation of the Treaty the Secretary of State presents to the House of Commons a report that the Republic of Mauritius has, in his or her view, not honoured the provisions of the Treaty they have undertaken to honour, and that the United Kingdom has presented to the Joint Commission a reasoned case that it believes the Republic of Mauritius has not honoured the provisions of the Treaty, and that the process in Article 14 of the Treaty has been exhausted, the Secretary of State must lay before the House of Commons, for its approval, a resolution to cease payments in connection with the Treaty.
9 Commencement and short title (1)

Except for sections 3 to 5 (as to which see section 1(2)), this Act comes into force on the day on which it is passed.

 (2)

This Act may be cited as the Diego Garcia Military Base and British Indian Ocean Territory Act 2026.
[]

Brought from the Commons on 21st October 2025

Ordered to be Printed, 5th January 2026.

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