What is in the Chagos Islands deal and why is it controversial?

Donald Trump has slammed the UK's decision to hand the Chagos Islands to Mauritius, in a deal that includes a formal transfer of Diego Garcia, home to a key US military base.

The US president said giving away the land was "an act of great stupidity", adding that the UK took the decision for "no reason whatsoever".

But the UK government is standing firm. In a statement on 20 January, an official spokesperson said the government acted because the base on Diego Garcia was "under threat after court decisions undermined our position and would have prevented it operating as intended in future".

"The UK will never compromise on our national security," the spokesperson added.

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The UK and Mauritius have agreed to the deal, but it is yet to be ratified (made officially valid) by the UK parliament, so the islands currently remain British territory.

So what is the deal really about, why has it sparked controversy and what does it mean for the UK-US military presence on the archipelago?

Where are the Chagos Islands?

The Chagos Islands are made up of more than 600 islands lying in the Indian Ocean, halfway between Africa and Indonesia. Around 4,000 people are stationed there.

Why are they so controversial?

The islands were a dependency of Mauritius when it was a French colony, but the UK claimed them as part of Mauritius in the early 19th Century and kept them beyond the country's independence in 1968.

In the early 1970s, the UK expelled everyone from the archipelago so the US could build a naval support facility on the biggest island, Diego Garcia.

Up to 2,000 native inhabitants, who are often referred to as Chagossians or Ilois, were removed to Mauritius or the Seychelles.

The expulsions are regarded as one of the most shameful parts of Britain's modern colonial history and Chagossians have spent decades fighting to return.

Why is the Diego Garcia base so important?

Diego Garcia serves as a key military base for both the US and UK.

It is leased to the US but operates as a joint UK-US base. Since 1971, only military employees have been allowed access.

The UK government said its "strategic location" made it "vital to UK and US power projection in the Indian Ocean and beyond". It is described as "a unique shared platform" enabling a UK-US military presence across the Middle East, Indo-Pacific and Africa.

Sir Keir Starmer has noted that it was used to deploy aircraft to "defeat terrorists in Iraq and Afghanistan".

More recent operations launched from the base include bombing strikes against ‍Houthi targets in Yemen in 2024 and 2025 and humanitarian aid deployments to Gaza.

Why did the UK agree to return the islands?

Mauritius and the UK have been in dispute over the islands for the past 50 years.

In 2010, Mauritius started proceedings against the UK to challenge the legality of how Britain had declared sovereignty, including its declaration of a marine protected area around the archipelago, which it argued stopped Chagossians from returning.

It demanded compensation and repatriation of former inhabitants.

In 2018, the fight made it to the International Court of Justice.

Under the Conservative government in 2022 sovereignty negotiations with Mauritius began, but halted a year later after a paper by three academics said transferring the islands would be a "major self-inflicted blow".

Two years later, in October 2024, the UK agreed to transfer sovereignty of the Chagos Islands to Mauritius. The deal, however, drew some criticism from lawmakers as ‌well as Britons born on Diego Garcia.

At the time, the US said it "welcomed the historic agreement", commending both countries' leaders for their vision.

In February ​2025, ahead of the signing, Mr Trump also expressed preliminary support for the deal. Canada, Australia, New Zealand and India have also backed the agreement.

What is in the final deal?

Last May, Sir Keir Starmer's Labour government signed a deal to return the islands, which would mean Britain formally gives up sovereignty of the Indian Ocean territory.

The deal states:

• The UK will hand sovereignty of the territory over to Mauritius and lease the Diego Garcia base from the Mauritian government over 99 years;
• It will ban other powers from using the islands around Diego Garcia without agreement with the UK;
• Mauritius will be free to arrange for resettlement of Chagossians on all islands except Diego Garcia;
• The period can be extended by a further 40 years, if both parties agree;
• Sir Keir said the average cost per year is £101m. Sky News analysis suggests the total cost could rise as high as £30bn;
• Both the Commons and the Mauritian parliament need to ratify the deal.

Sir Keir said the UK might otherwise have lost the island over Mauritius's legal claim on the Chagos Islands, which may have allowed hostile countries to set up their own bases or carry out exercises.

The government said the final deal also addressed "wrongs of the past" and demonstrated "the commitment of both parties to support the welfare" of Chagossians.

Why is there concern over the deal?

Concerns over the deal include any future Mauritian government not adhering to the agreement and subsequently allowing China, which is heavily invested in Mauritius, to take over the base.

US Secretary of State Marco Rubio echoed these concerns in February last year, saying the deal could cause potential threats to US security.

While Conservative Party leader Kemi Badenoch said the deal made "us and ​our NATO allies weaker".

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Some Chagossians, many of whom ended up living in Britain after being removed from the archipelago, have protested against the agreement on the grounds that they were not consulted on its detail.

The UK's House of Lords also objected to elements of the deal in January of this year. The House inflicted four defeats over the details of the leasing of Diego Garcia and the publication of any detailed payments made to Mauritius.

(c) Sky News 2026: What is in the Chagos Islands deal and why is it controversial?