Threads / Diego Garcia Military Base and British Indian Ocean Territory Bill / Diego Garcia Military Base and British Indian Ocean Territo…

Research & Analysis Published 19 Jan 2026 House of Commons Library ↗ View on Parliament

Diego Garcia Military Base and British Indian Ocean Territory Bill: Consideration of Lords amendments

Type: Commons Briefing Paper (CBP-10464) The House of Commons will consider Lord's amendments to the Diego Garcia Military Base and British Ocean Territory Bill on 20 January 2026.

Attachments

↓ CBP-10464.pdf
application/pdf

▤ Verbatim text from source document

Diego Garcia Military Base and British Indian Ocean Territory BillConsideration of Lords amendments - House of Commons Library

Documents to download

Diego Garcia Military Base and British Indian Ocean Territory BillConsideration of Lords amendments
(3 MB
, PDF)

Download full report

Download ‘Diego Garcia Military Base and British Indian Ocean Territory BillConsideration of Lords amendments’ report (3 MB
, PDF)

The
Diego Garcia Military Base and British Indian Ocean Territory Bill 2024-25
is a government bill (bill 285 of the 2024–25 parliamentary session).

The bill’s primary purpose is to implement in UK law certain provisions of the
treaty signed in May 2025 between the UK and Mauritius
agreeing the status and future of the Chagos Archipelago, including the joint US–UK military base on Diego Garcia (the archipelago’s largest island). The UK currently administers the Chagos Archipelago as the British Indian Ocean Territory (BIOT), one of the UK’s 14 Overseas Territories.

It has now completed all its Commons and Lords stages and was amended during its Lords stages. This briefing provides an overview of Lords amendments agreed and added to the bill.

Amendments the government is opposing

The Foreign Secretary, Yvette Cooper has tabled
motions to disagree the following amendments
, to be considered in the House of Commons on 20 January 2026:

Amendment 1 would require the Secretary of State to negotiate an amendment to the treaty so the UK could stop making payments to the Mauritian Government in the event that it cannot use the Diego Garcia Military base.

Amendments 2 and 3 would require the holding of a referendum for Chagossians on the terms of the treaty.

Amendment 5 would require the Secretary of State to publish a statement setting out the total costs of payments to Mauritius under the treaty, and the methodology used to calculate those costs

Amendment 6 would require the Secretary of State to lay an estimate of the anticipated expenditure related to the treaty before the House of Commons. In the event of Mauritius not honouring the provisions of the treaty, where all dispute mechanisms have been exhausted, the amendment would require the Secretary of State to lay before the House of commons a resolution to cease payments under the treaty.

There was also a government amendment (now amendment 4) made at the Lords third reading of the bill, this requires that any orders made under Clause 6 of the bill be subject to the
negative procedure
. This amendment responded to
recommendations made by the Delegated Powers and Regulatory Reform committee
.

Main provisions of the UK–Mauritius treaty

The treaty provides for
Mauritius to exercise full sovereignty over the Chagos Archipelago
, with the UK exercising rights on Diego Garcia during an initial 99-year period. Over the 99 years, the UK will pay Mauritius a total of around £3.4 billion in 2025/26 prices. The UK Government says this resolves
the long-standing BIOT sovereignty dispute
and secures the military base for continued operations in the long term.

Further details of the treaty are set out in Library briefing
2025 treaty on the British Indian Ocean Territory/Chagos Archipelago
.

The bill gives domestic effect to the treaty

Under the UK’s constitution, it’s formal rights and duties under international law do not automatically change its domestic law. Legislation is therefore sometimes needed to give domestic effect to new treaty-based rights and duties that the government has agreed to.

This bill contains the provisions of the treaty that require changes to UK law. These include:

terminating the UK’s sovereignty over the BIOT but providing for the continued administration of Diego Garcia by the UK

revoking UK legislation that provides the BIOT’s constitution and certain provisions relating to citizenship status of those connected to the BIOT

providing powers to implement the treaty using the Crown’s prerogative powers through Orders in Council

saving existing laws applying to the BIOT and applying them to Diego Garcia, except for British nationality law

removing the ability of people to acquire British Overseas Territories citizenship on the basis of connection to the BIOT, while preserving a route to full British citizenship for Chagossian descendants

Commons debate on the bill

The bill had its second reading on 9 September 2025, and a committee of the whole House and all other remaining Commons stages took place on 20 October 2025.

During committee stage consideration of the bill, two amendments and a new clause were put to a division but were not added to the bill:

Amendment 7 was tabled by Priti Patel, the Shadow Foreign Secretary, and sought to require the government to lay a memorandum before Parliament on the international law requirements for it to cede sovereignty of the British Indian Ocean Territory (BIOT) before the bill could come into force.

Amendment 9 was tabled by Liberal Democrat spokesperson, Dr Al Pinkerton, and sought to require that the government negotiate with the Mauritian Government on a right for Chagossians to return to the BIOT, and on a referendum on the treaty. It would have required the government to lay a report on these negotiations before Parliament.

New Clause 1 was tabled by Priti Patel and sought to require parliamentary approval for any payments made under the treaty to Mauritius.

The House also divided on whether clause 2 (the clause formally ceding the UK’s sovereignty over BIOT) should stand part of the bill, with 318 MPs voting in favour and 174 against.