UK House of Lords Begins Committee Stage for Bill Transferring BIOT Sovereignty to Mauritius

House of Lords Scrutinizes BIOT Sovereignty Bill

The UK Parliament's House of Lords has begun its Committee Stage examination of the Diego Garcia Military Base and British Indian Ocean Territory Bill. This crucial legislative step aims to implement provisions of a treaty signed in May 2025 between the United Kingdom and Mauritius, which addresses the long-disputed sovereignty of the Chagos Archipelago, also known as the British Indian Ocean Territory (BIOT). The bill seeks to terminate UK sovereignty over the territory while securing the future of the vital joint UK-US military base on Diego Garcia.

Historical Context and International Rulings

The Chagos Archipelago's status has been a contentious issue for decades. The UK separated the islands from Mauritius in 1965, three years before Mauritius gained independence, to establish the BIOT. Between 1968 and 1973, approximately 1,500 to 2,000 Chagossians, the indigenous inhabitants, were forcibly removed from their homes to facilitate the construction of the US military base on Diego Garcia. This displacement has been widely condemned, with many Chagossians still seeking the right to return.

International legal bodies have consistently challenged the UK's claim to the territory. In 2019, the International Court of Justice (ICJ) issued an advisory opinion stating that the UK's administration of the Chagos Archipelago was unlawful and that it should return the islands to Mauritius 'as rapidly as possible'. This was followed by a United Nations General Assembly resolution endorsing the ICJ's opinion. In 2021, the International Tribunal for the Law of the Sea (ITLOS) also ruled in favour of Mauritius's sovereignty claim.

Key Provisions of the New Agreement

The treaty, announced in October 2024 and signed in May 2025, represents a significant shift in the UK's stance. Under the agreement, Mauritius will exercise full sovereignty over the Chagos Archipelago. However, the UK will retain control and administer the Diego Garcia military base for an initial period of 99 years, with provisions for extension. The UK government has committed to paying Mauritius approximately £3.4 billion over this 99-year period.

A key aspect of the agreement is the provision for the return of Chagossians to islands within the archipelago, excluding Diego Garcia. A trust fund, capitalized by the UK, will be established to support their resettlement. The UK government has stated that this agreement resolves the long-standing sovereignty dispute and secures the future of the military base, which it considers a 'vital UK national asset'.

Parliamentary Scrutiny and Concerns

The bill was introduced on July 15, 2025, and underwent its second reading in the House of Commons on September 9, 2025, before completing its Commons stages on October 20, 2025. The House of Lords began its Committee Stage on Tuesday, November 18, 2025, with a second day scheduled for November 25, 2025. During this stage, peers will conduct a line-by-line examination of the bill, considering potential amendments to its clauses.

The legislation has not been without its critics. Some, including Conservative Shadow Foreign Secretary Dame Priti Patel MP, have introduced a Private Members' Bill aimed at blocking what they term the 'Chagos Surrender Deal'. Concerns have been raised regarding the perceived lack of consultation with British Chagossians, the financial implications for UK taxpayers, and the potential impact on national security. A 'tactical retreat' by the government on November 10, 2025, regarding a committal motion in the Lords, indicated potential opposition to aspects of the bill.