British Indian Ocean Territory: 2024 UK and Mauritius agreement

On 3 October 2024, the UK and Mauritian governments announced they had reached an agreement on the sovereignty of the British Indian Ocean Territory (BIOT), also known as the Chagos Archipelago. Negotiations began in November 2022 under the government of Rishi Sunak.

This briefing focuses on the October 2024 agreement between the UK and Mauritius, the reaction to it, and how it may be scrutinised by Parliament.

What is the BIOT?

The BIOT is one of 14 British Overseas Territories. Located in the Indian Ocean, it is made up of the Chagos Archipelago of islands, including the biggest island, Diego Garcia, the site of a joint US-UK military base.

From 1968 to 1973, the UK removed the local population (estimated to have been between 1,400 and 1,700 people), known as Chagossians or Ilois, to establish the military base. Many were resettled in Mauritius, the Seychelles, and, from 2002, in the UK (PDF). Laws made by the UK’s Commissioner made it illegal to stay or return without permission.

The UK has apologised for the nature of their removal, and announced three payments to support their resettlement, with the most recent in 2016.

What is in the agreement?

Under the terms of the proposed UK-Mauritius treaty, the UK and Mauritius will agree that Mauritius is sovereign over the Chagos Archipelago, including Diego Garcia. At the same time, the UK will, for a 99-year initial period (which can be extended), exercise “the sovereign rights and authorities of Mauritius required to ensure the continued operation of the [Diego Garcia military] base well into the next century”.

Other significant parts of the agreement include:

• cooperation between the UK and Mauritius on environmental protection, maritime security and combating illegal fishing, as well as the creation of a Mauritian Marine Protected Area (the BIOT currently has its own Marine Protected Area)
• funding from the UK to Mauritius in return for the use of Diego Garcia and for infrastructure projects to “enable” a new “economic, security and environmental partnership” between the two countries
• Mauritius will be free to implement a resettlement programme to the outer islands, but not Diego Garcia
• Mauritius and the UK will establish a new programme of visits to the archipelago for Chagossians
• the UK and Mauritius will establish a new trust fund “for the benefit of Chagossians”, capitalised by the UK
• the UK Government will provide additional support for Chagossians living in the UK

The agreement is currently being drawn up into a treaty (a legally binding agreement in international law), the text of which is expected to be published in the coming weeks. The UK Government will also introduce legislation to implement parts of the treaty in domestic (UK) law. The government has said the treaty and bill will be subject to scrutiny in the UK Parliament, and that it intends to pursue ratification of the treaty in 2025.

Separate to the UK-Mauritius agreement, on 15 October the UK Government signed a memorandum of understanding (MoU) with the British Overseas Territory of St Helena. In the MoU the St Helena Government agreed it would house any migrants arriving at the BIOT until the UK-Mauritius treaty comes into force, at that time Mauritius becomes responsible for any migrants. The UK Government says there have been no arrivals at the BIOT since 2022 and this is a “contingency measure only”.

Why is the BIOT disputed?

The BIOT has been the subject of long-running legal disputes focused primarily on two issues:

• The exercise of sovereignty over the BIOT since it was created as a legal entity by the UK in 1965, detaching the Chagos Archipelago from its colony Mauritius. From the 1980s onwards, Mauritius advanced its claims to sovereignty over the islands in international forums. The UK Government undertook that it would “cede sovereignty of the territory to Mauritius” once the BIOT was “no longer required for defence purposes”.
• The rights of the inhabitants of the Chagos Archipelago and their descendants to return to live on the islands after they were removed by the UK Government between 1968 and 1973.

These disputes and the origin of the recent negotiations between the UK and Mauritius are explored in more detail in the following Library briefings:

• British Indian Ocean Territory: UK to negotiate sovereignty 2022/23, November 2022
• Disputes over the British Indian Ocean Territory: February 2021 update, February 2021
• Disputes over the British Indian Ocean Territory: December 2019 update December 2019
• Disputes over the British Indian Ocean Territory: a survey, May 2013