Britain’s Chagos Deal Can’t Go Forward Without U.S. Consent

By Richard Ekins

Friday, January 30, 2026

 

Up until January 20, the British government was on track to ratify the United Kingdom’s agreement to transfer sovereignty of the Chagos Archipelago to Mauritius, with the U.K. leasing back Diego Garcia for 99 years so that the joint U.S.-U.K. military base could stay in business. But recent remarks by President Donald Trump and other senior members of his administration raise serious doubts about whether the agreement will ever be ratified.

 

This is not the first twist in the sorry tale of Britain’s recent attempt to pay billions for the privilege of surrendering a priceless strategic asset while degrading U.S.-U.K. defense interests along the way. But it may be that the tale is nearing its end, because without American consent, the Chagos deal cannot go ahead.

 

Transferring sovereignty to Mauritius would breach the terms of a 1966 exchange of notes between the U.K. and the U.S. “concerning the availability of the British Indian Ocean Territory for defense purposes.” Unless and until the United States agrees to change the 1966 agreement, which is a binding treaty under international law, the U.K. cannot lawfully surrender the Islands.

 

In October 2023, my colleagues and I published a paper for Britain’s leading think tank, Policy Exchange, critiquing the then-Conservative government’s willingness to consider ceding the Chagos Islands to Mauritius. We pointed out the strategic significance of the Islands and the weakness of Mauritius’s sovereignty claim. The U.K. was at risk of surrendering to Mauritian lawfare, we said, and was giving far too much weight to a purely advisory opinion of the International Court of Justice.

 

Senior figures in the Conservative government listened, and negotiations were paused, with no agreement with Mauritius reached by the time the Conservatives left office in July 2024. But the new Labour government moved very quickly, reaching an agreement in principle with Mauritius in early October 2024, shortly before elections in Mauritius and, of course, in the United States.

 

The Mauritian government that had negotiated the agreement was thrown out of office, which briefly put the agreement’s future in doubt. But the new government returned to the table, and an agreement was signed in May 2025. Still, the election of President Trump in November 2024 introduced fresh doubt, with then-Foreign Secretary David Lammy saying: “If President Trump doesn’t like the deal, the deal will not go forward.”

 

Intense British diplomacy seemed to yield fruit, with Trump initially saying that the lease agreement seemed fine and Secretary of State Marco Rubio issuing a statement in May 2025 welcoming the deal, despite reports that the administration harbored private doubts about its merits. In June, the British government began the long process of trying to persuade Parliament to enact the legislation — a necessary legal precondition for the treaty with Mauritius to be ratified.

 

Members of the House of Lords, Parliament’s upper house, put up a good fight: They amended the draft legislation in important ways and imposed some preconditions on ratification. But the government has a large majority in the House of Commons, and so it seemed inevitable that the legislation would be enacted and the government would ratify the treaty.

 

But just last week, President Trump threw a wrench into the Labour government’s plans with a statement denouncing the surrender of the Chagos Islands to Mauritius as “an act of great stupidity.” Treasury Secretary Scott Bessent followed up, saying that the U.K. was letting down the U.S. by handing over the archipelago to Mauritius.

 

Prime Minister Keir Starmer’s initial response was robust. Speaking in Parliament on January 21, he claimed that the president’s statement was made to try to pressure Britain into abandoning Greenland. A cabinet minister, Steve Reed, has since added that because the U.K.’s position on Greenland will not change, he suspects that President Trump will not pursue the Chagos point further.

 

This may be wishful thinking. American support for the surrender of sovereignty to Mauritius is not just a political necessity — it is also a legal requirement. Article 1 of the 1966 treaty provides that “the Territory shall remain under United Kingdom sovereignty.” What this means is that unless and until the 1966 treaty is formally amended, the U.K. cannot ratify its agreement with Mauritius, which would give up British sovereignty over the Chagos Islands, without breaching international law and without wronging its closest ally.

 

The U.K.-U.S. joint base on Diego Garcia is critical to security in the Indo-Pacific. British sovereignty over the Chagos Islands was thought to be necessary for the establishment of the base and remains fundamental to its secure operation, now and for the foreseeable future. In considering whether to amend the 1966 treaty, the Trump administration should ask whether replacing British sovereignty with Mauritian sovereignty is in America’s defense interests.

 

The British government will be energetically attempting to persuade the Trump administration that the agreement that it has reached with Mauritius is essential to protect the future of Diego Garcia. But as I’ve recently argued, in another paper for Policy Exchange, the base is secure if the Chagos Islands remain sovereign British territory, while its fate is uncertain if is the Islands are transferred to Mauritius.

 

The risks of walking away from the deal have been greatly exaggerated. No international tribunal has the authority to rule that Mauritius is sovereign over the Chagos Islands or to require the U.K. to cede the islands to Mauritius. If any international tribunal in some other context, such as the law of the sea, takes for granted that Mauritius is sovereign, its ruling will be fundamentally misconceived — and the U.K. should refuse to comply. If Mauritius were to attempt to frustrate U.S.-U.K. defense interests — say, by taking payments from our adversaries to enable their incursion into the archipelago — it would prove itself to be a hostile state and should be treated as such.

 

The risks of handing over sovereignty to Mauritius have been greatly underappreciated. The terms of the new treaty do not provide the U.K. with a veto over Mauritian actions in the archipelago, and Britain will have no recourse if Mauritius fails to comply with its obligations. If the Chagos Islands become Mauritian territory, Mauritius will be an even more attractive target for Chinese subversion. The treaty assumes the goodwill of future Mauritian governments, which is by no means guaranteed.

 

The agreement with Mauritius also introduces significant new legal risks. The treaty requires the U.K. to veto military action emanating from Diego Garcia if such force does not comply with international law. It also requires the U.K. to give notice about the use of force to Mauritius, arguably even before operations are carried out. If Mauritius, perhaps at China’s behest, claims that the U.K. has breached these obligations, it may take countermeasures that would have a very significant negative impact on U.S.-U.K. defense interests. Further, if the treaty is ratified, then the Chagos Islands will be Mauritian territory, and Mauritius will have an obligation under the Treaty of Pelindaba to prohibit the stationing of nuclear weapons on Diego Garcia, as Mauritius’s deputy prime minister has publicly confirmed.

 

It now falls to the United States to decide whether to agree to amend the 1966 treaty and to clear the way for the U.K. to ratify its agreement with Mauritius. Both the British government and the Trump administration should reflect on the strategic importance of Diego Garcia and the risks of Mauritian sovereignty. They should resolve to maintain the U.K.’s sovereign rights over the Chagos Islands, robustly resisting lawfare that threatens to undermine our collective defense.