UK House of Lords Debates Bill to Transfer BIOT Sovereignty to Mauritius, Securing Diego Garcia Base

House of Lords Examines Landmark Sovereignty Bill

The United Kingdom Parliament's House of Lords is currently undertaking the Committee Stage for the Diego Garcia Military Base and British Indian Ocean Territory Bill. This crucial legislation is designed to enact the provisions of a treaty signed in May 2025 between the UK and Mauritius, which seeks to resolve a long-standing dispute over the sovereignty of the Chagos Archipelago. The bill's examination in the Lords began on Tuesday, November 18, 2025, with a second sitting scheduled for November 25.

The primary objective of the bill is to terminate UK sovereignty over the British Indian Ocean Territory (BIOT), which encompasses the Chagos Archipelago, and to amend existing legislation to reflect its new status. Concurrently, it provides for the continued administration and operation of the joint UK-US military base located on Diego Garcia, the largest island in the archipelago.

Historical Context of the Chagos Archipelago Dispute

The Chagos Archipelago has been a point of contention for decades. In 1965, the United Kingdom detached the islands from Mauritius, then a British colony, to establish the BIOT, ahead of Mauritius's independence in 1968.

Between 1968 and 1973, the indigenous inhabitants, known as the Chagossians, were forcibly removed from their homes to make way for the construction of the US military base on Diego Garcia. This expulsion has been widely condemned, with Human Rights Watch describing it as an 'appalling colonial crime' and a 'crime against humanity'.

International legal bodies, including the International Court of Justice (ICJ) and the International Tribunal for the Law of the Sea (ITLOS), have issued advisory opinions and rulings stating that the UK has an obligation to return the islands to Mauritius, affirming that the UK has no sovereignty over the Chagos Archipelago.

Key Provisions of the UK-Mauritius Treaty

The treaty, signed on May 22, 2025, and now being implemented through this bill, outlines several critical agreements:

• Sovereignty Transfer: The UK will agree that Mauritius is sovereign over the entire Chagos Archipelago, including Diego Garcia.
• Diego Garcia Base: The UK will retain the right to exercise authority over the Diego Garcia military base for an initial period of 99 years, with an option to extend for a further 40 years. This ensures the continued, secure, and effective operation of the base, which is considered vital for regional and global security.
• Financial Compensation: The UK will pay Mauritius an annual average of £101 million for 99 years, amounting to approximately £3.4 billion in 2025/26 prices.
• Chagossian Welfare: The treaty commits both parties to support the welfare of Chagossians. Mauritius will be free to implement a program of resettlement on the islands of the Chagos Archipelago, excluding Diego Garcia. The UK will also capitalize a new trust fund for the benefit of Chagossians.
• Regional Cooperation: The agreement also includes provisions for cooperation on environmental protection, maritime security, and combating illegal fishing within the archipelago.

Parliamentary Scrutiny and Future Implications

The Diego Garcia Military Base and British Indian Ocean Territory Bill was introduced on July 15, 2025, and received its second reading on September 9, 2025. During the Committee Stage in the House of Lords, members are conducting a line-by-line examination of the bill, considering proposed amendments. These amendments include discussions on the Secretary of State's duties regarding Diego Garcia and the reasons for payments to the government of Mauritius.

The agreement has been endorsed by the United States, which recognized the strategic importance of the Diego Garcia base. US officials have praised the deal for securing the long-term operational capabilities of the joint military facility. The bill's passage is a significant step towards formally concluding a complex chapter in the UK's colonial history and establishing a new framework for the future of the Chagos Archipelago.