Britain has signed a deal to cede sovereignty of the Chagos Islands to Mauritius, after a London judge overturned a last-minute injunction and cleared the way for an agreement the government says is vital to protect the nation's security.

The multibillion-dollar deal will allow Britain to retain control of the strategically important US-UK air base on Diego Garcia, the largest island of the archipelago in the Indian Ocean, under a 99-year lease.

The signing went ahead after a carefully choreographed ceremony was postponed when lawyers representing a British national born in the Chagos Islands were granted an interim injunction at the High Court in the early morning hours.

Judge Martin Chamberlain then lifted that injunction following a hearing, saying Britain's interests would be "substantially prejudiced" if the injunction were to continue.

The government, which has been criticised by opposition parties for pursuing a deal they say is overly costly and would play into the hands of China, has long said the agreement is essential to secure the future of Diego Garcia.

"The strategic location of this base is of the utmost significance to Britain, from deploying aircraft to defeat terrorists in Iraq and Afghanistan to anticipating threats in the Red Sea and the Indo-Pacific," Prime Minister Keir Starmer told a news conference.

"By agreeing to this deal now, on our terms, we're securing strong protections, including from malign influence, that will allow the base to operate well into the next century."

The signing ends months of wrangling over the deal, the details of which were first announced in October, after the then-Mauritian leader Pravind Jugnauth was replaced by Prime Minister Navin Ramgoolam, who raised concerns about it.

It was further delayed after the inauguration of US President Donald Trump in January, with London wanting to give the new administration time to examine the details of the plan. In February, Trump indicated his backing for the deal.

Latest legal challenge 

The injunction was the latest legal challenge to the deal in the past two decades brought by members of the wider Chagossian diaspora, many of whom ended up in Britain after being forcibly removed from the archipelago more than 50 years ago.

It was granted following action by Bertrice Pompe, a British national who was born in Diego Garcia and has criticised the deal for excluding Chagossians.

James Eadie, the government's lawyer, said the delay was damaging to British interests and "there is jeopardy to our international relations ... (including with) our most important security and intelligence partner, the US."

A military airstrip on Diego Garcia. – file

It is one less headache for Starmer, who is under fire from his own governing Labour Party for implementing welfare cuts to try to better balance Britain's books.

But Starmer's political opponents were again critical of the accord, arguing it was both costly and by ceding sovereignty, China could further deepen its ties with Mauritius, benefiting Beijing's influence in the Indian Ocean.

Conservative Party foreign affairs spokeswoman Priti Patel wrote on X:

"Labour's Chagos Surrender Deal is bad for our defence and security interests, bad for British taxpayers and bad for British Chagossians."

The financial component of the deal includes £3 billion to be paid by Britain to Mauritius over the 99-year term of the agreement, with an option for a 50-year extension and Britain maintaining the right of first refusal thereafter.

The base's capabilities are extensive and strategically crucial. Recent operations launched from Diego Garcia include bombing strikes on Houthi targets in Yemen in 2024-2025, humanitarian aid deployments to Gaza and, further back, attacks on Taliban and al-Qaeda targets in Afghanistan in 2001.

Key facts about the deal 

Here are some key points about the islands, the deal and why it remains contentious:

Islanders displaced 

The Chagos Archipelago is a group of six atolls with more than 600 individual islands in the Indian Ocean, 500 kilometres (300 miles) south of the Maldives and halfway between Africa and Indonesia.

Around 4000 people are stationed on the islands now.

No indigenous inhabitants, often referred to as Chagossians or Ilois, have lived there since Britain forcibly displaced up to 2000 people, mostly former agricultural workers, from the islands in the late 1960s and early 1970s to establish the Diego Garcia base.

Britain has since come under increasing international pressure to hand over control of the islands to Mauritius.

But a handover agreement reached last October has drawn criticism from MPs as well as Britons born on Diego Garcia.

The deal

In October, Britain agreed to transfer sovereignty of the Chagos Islands to Mauritius, a former colony that gained independence in 1968.

Britain would pay Mauritius £3 billion (US$4 billion) to secure the future of the Diego Garcia military base as part of that deal, US officials have said.

Despite the transfer of sovereignty, Britain would maintain control over the base under a 99-year lease.

US President Donald Trump backed the deal in February.

Significance 

The deal is significant due to the strategic importance of Diego Garcia, which serves as a key military base in the Indian Ocean for the US and Britain. China also has a growing reach in the region, including close trade ties with Mauritius.

Recent operations launched from Diego Garcia include bombing strikes against Houthi targets in Yemen in 2024 and 2025, humanitarian aid deployments to Gaza and attacks against Taliban and al-Qaeda targets in Afghanistan in 2001.

UN court's view 

In 2019, after a request by the United Nations General Assembly, the UN's top court issued a non-binding ruling calling on Britain to give up control of the archipelago after wrongfully forcing the population to leave in the 1970s to make way for the US base.

Britain split the archipelago off from its colonial island territory of Mauritius in 1965, three years before granting independence to Mauritius – minus the islands. The International Court of Justice said that split was unlawful.

Concerns

US Secretary of State Marco Rubio raised concerns in February about potential threats to US security, particularly in light of China's influence in the region.

Mauritian Prime Minister Navin Ramgoolam, who was elected after the initial agreement was reached, questioned it when he took office. Ramgoolam had wanted Trump to look at the plan and say whether it was a good arrangement.

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.

Kemi Badenoch, leader of the opposition in Britain, previously vowed to oppose the deal and has said it was not in Britain's national interest.

Legal challenge 

A UK High Court judge issued a last-minute injunction on Thursday, halting the government's plan to sign the deal with Mauritius.

The injunction was sought by Bernadette Dugasse and Bertrice Pompe, British nationals who were born in Diego Garcia.

The pair have criticised the deal for excluding Chagossians.

The injunction was overturned hours later by Britain's High Court, clearing the way for the deal to be signed.

Bertrice Pompe and Bernadette Dugasse. – Reuters

What to know about the disputed islands

What are the Chagos Islands and why are they contested?

The remote chain of more than 60 islands is located in the middle of the Indian Ocean off the tip of India, south of the Maldives.

The Chagos Islands have been under British control since 1814, when they were ceded by France.

The archipelago is best known for the military base on Diego Garcia, which has supported US military operations from Vietnam to Iraq and Afghanistan. In 2008, the US acknowledged it also had been used for clandestine rendition flights of terror suspects.

Britain split the Chagos Islands away from Mauritius, a former British colony, in 1965 – three years before Mauritius gained independence – and called the Chagos archipelago the British Indian Ocean Territory.

In the 1960s and 1970s Britain evicted as many as 2000 people from the islands so the US military could build the Diego Garcia base.

The US has described the base, which is home to about 2500 mostly American personnel, as “an all but indispensable platform” for security operations in the Middle East, South Asia and East Africa.

Most recently, the US deployed several nuclear-capable B-2 Spirit bombers to Diego Garcia amid an intense airstrike campaign targeting Yemen’s Houthi rebels.

In recent years criticism grew over Britain's control of the archipelago and the way it forcibly displaced the local population. The United Nations and the International Court of Justice have both urged Britain to end its “colonial administration” of the islands and transfer their sovereignty to Mauritius.

What is in the deal and why was it delayed?

In October Britain's government announced that it was finalising details of a treaty to hand sovereignty of the islands to Mauritius, with the exception of Diego Garcia, which will remain under British control for at least 99 years.

The deal was hailed by then-US President Joe Biden as a “historic agreement” that secured the future of the Diego Garcia base. But Britain's opposition Conservatives slammed the government for surrendering control of the territory, saying that the decision exposed the UK and its allies to security threats. Last year the now-Secretary of State Marco Rubio also said it posed “a serious threat” to US national security.

In January, Britain’s government confirmed that the Trump administration was reviewing a renegotiated deal, without providing details.

In February, Trump suggested he was in favour of the agreement when he met with British Prime Minister Keir Starmer in Washington.

Meanwhile, voters in Mauritius ousted the government that made the deal, and new Prime Minister Navin Ramgoolam backed away from it, citing financial concerns.

Ramgoolam suggested that the initial deal – which would reportedly see the UK pay £90 million a year to Mauritius for the continued operation of the Diego Garcia military base – was a “sellout". The UK government has not disclosed how much it will pay to lease the base.

After more negotiations, a final deal was set to be signed by the two countries' leaders on Thursday.

What does the deal mean for displaced islanders?

An estimated 10,000 displaced Chagossians and their descendants now live primarily in Britain, Mauritius and the Seychelles. Many of them want to return to the islands, and some have fought unsuccessfully in UK courts for many years for the right to go home.

Chagossians say they were left out of the political negotiations, which have left them unclear on whether they and their descendants could ever be allowed to return to their homeland.

Human Rights Watch has said that Britain's forced displacement of the Chagossians and ongoing refusal to let them go home “amount to crimes against humanity committed by a colonial power against an Indigenous people”.

The draft deal stated a resettlement fund would be created for displaced islanders to help them move back to the islands, apart from Diego Garcia. But details of how that will work remain sketchy.

Two Chagossian women, Bernadette Dugasse and Bertrice Pompe, challenged the handover deal in the British courts. They argued it would become even harder to return once Mauritius takes control of the islands.

Thursday's court injunction was granted in response to their application.