The Chagos deal: every step from 1965 to today, and what it would mean for Mauritius
A treaty signed in May 2025 recognises Mauritian sovereignty over the Chagos Archipelago and keeps the Diego Garcia base for 99 years, but it has not entered into force. The full timeline, the terms, the money, and where things stand in October 2026.
In short
In 1965, three years before independence, Britain detached the Chagos Archipelago from Mauritius and between 1967 and 1973 expelled about 2,000 Chagossians to make way for a US military base on Diego Garcia.
Mauritius won the legal battle: the ICJ advisory opinion (2019, 13-1) found the separation unlawful, the UN General Assembly backed it (116 votes), and the ITLOS treated Mauritius as the coastal state (2021).
On 22 May 2025 the UK and Mauritius signed a treaty: Mauritius is sovereign over the whole archipelago; the UK keeps Diego Garcia for 99 years (extendable by 40) and pays about £101 million a year on average, plus a £40 million Chagossian trust fund and £45 million a year for development for 25 years.
The treaty has not entered into force. After US President Trump turned against it in early 2026, the UK let the implementing bill lapse in April 2026; it was not carried into the new session.
As of early October 2026, talks have resumed: the UK says it will work with Mauritius and the US on a way forward, Prime Minister Ramgoolam met UK officials in London on 26 September, and Mauritius calls its sovereignty “non-negotiable”.
From 1965 to the courts
In November 1965, during independence talks, Britain separated the Chagos Archipelago from the colony of Mauritius to create the British Indian Ocean Territory, paying £3 million. Mauritius became independent on 12 March 1968 without it. Between 1967 and 1973 the islanders, about 2,000 people, were removed to Mauritius and Seychelles, and Diego Garcia became a major US military base.
For decades Mauritius pursued its claim through diplomacy and then the courts. In 2015 an arbitral tribunal ruled that the UK's 2010 Marine Protected Area around the islands breached international law. In 2017 the UN General Assembly asked the International Court of Justice for an opinion; in February 2019 the Court found, by 13 votes to 1, that the decolonisation of Mauritius had not been lawfully completed and that the UK should end its administration “as rapidly as possible”. The General Assembly endorsed this in Resolution 73/295 in May 2019, and in 2021 a special chamber of the Law of the Sea tribunal treated Mauritius as the coastal state in a maritime-boundary case with the Maldives.
What the 2025 treaty says
The treaty recognises that Mauritius is sovereign over the entire Chagos Archipelago, including Diego Garcia. Mauritius in turn grants the UK the right to exercise sovereign rights over Diego Garcia so that the joint UK-US base can keep operating for an initial 99 years, extendable by a further 40 years and beyond if both agree.
Around Diego Garcia there are security provisions, including restrictions on other countries' activities in the outer islands without UK agreement. Mauritius is free to resettle Chagossians on the outer islands (but not Diego Garcia), and the treaty provides for cooperation on the marine environment.
What it would bring Mauritius
At today's exchange rate (about Rs 62 per pound), the first three years' payments of £165 million are worth roughly Rs 10 billion a year: about 1.3% of GDP, comparable to the entire Coastal Erosion Adaptation Programme every five months. The development framework adds about Rs 2.8 billion a year for 25 years. For a country with public debt around 87% of GDP, this is significant, predictable foreign-currency income, and Prime Minister Ramgoolam has linked it to income-tax relief.
Beyond money: completing decolonisation; control of a vast exclusive economic zone (fishing licences, marine research, conservation); the chance for Chagossians and their descendants to return to the outer islands; and a stronger diplomatic position in the Indian Ocean.
There are costs and risks: resettlement on remote, low-lying atolls is expensive and exposed to sea-level rise; Chagossian communities are divided over the deal and some want their own say; and Mauritius must manage relations with the US, the UK, India and the Maldives (with which it broke diplomatic relations in February 2026 over the dispute).
Where things stand (October 2026)
The treaty requires ratification by both countries and an exchange of letters with the United States under the 1966 UK-US agreement on the base. In the UK, the Diego Garcia Military Base and British Indian Ocean Territory Bill passed the House of Lords in January 2026 with an amendment, requiring the UK to stop paying if it cannot use the base, which the Commons rejected.
In January and February 2026 President Trump turned against the deal, and the US did not provide its consent. In April 2026 the UK Government told Parliament the bill could not complete its passage before the session ended on 29 April; it was not included in the new session's legislative programme. Mauritius said it would use every diplomatic and legal avenue.
In September 2026 the issue returned: on 21 September the UK Prime Minister said Britain would work with Mauritius and the US on a way forward that secures Diego Garcia; on 26 September Prime Minister Ramgoolam travelled to London for talks with the UK National Security Adviser, Jonathan Powell; and at the UN General Assembly Foreign Minister Dhananjay Ramful called Mauritius' sovereignty “non-negotiable”. No new timetable for ratification has been announced.