Chagos Sovereignty Deal Faces New Security Questions After Pelindaba Treaty Concerns Raised in Commons

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The United Kingdom’s controversial agreement to transfer sovereignty of the Chagos Archipelago, including the strategically vital island of Diego Garcia, to Mauritius has come under renewed scrutiny this week after new information emerged about the implications of African nuclear-weapons-free zone commitments for Western security cooperation.

In a Commons session on Tuesday, several Labour MPs admitted they were unaware of the relevance of the African Nuclear-Weapon-Free Zone Treaty, commonly known as the Pelindaba Treaty, to the Chagos deal, triggering calls from across Parliament for the process to be paused until all members fully understand the risks involved.

The Pelindaba Treaty prohibits the stationing, possession, testing or transit of nuclear weapons on the territory of its signatories. Mauritius, which would assume sovereignty over the Chagos Islands under the treaty agreed with the UK in May 2025, is a party to that agreement. Once the archipelago becomes Mauritian territory, territory that is part of the African nuclear-weapons-free zone could in principle be subject to inspections to verify compliance with the treaty’s terms. 

Under current arrangements, the UK and United States operate a joint military base on Diego Garcia, which is regarded as a key strategic hub for operations in the Indian Ocean, Middle East and Asia Pacific. The base has historically hosted nuclear-capable assets and nuclear-armed submarines as part of broader Western deterrence and naval strategy. 

Critics, including a number of Conservative peers and defence analysts, have warned that once Diego Garcia is formally Mauritian territory and subject to the Pelindaba Treaty, the United States and its allies could, under the treaty’s inspection mechanisms, face demands from Mauritius or other signatories to open the base to verification. Prohibitions on nuclear weapons under the treaty extend to territory of signatories, raising the prospect that nuclear-related operations could be legally constrained. 

“The Pelindaba Treaty seems pretty clear that it excludes the use of any part of any African country,” a senior critic of the deal told parliamentary reporters earlier this month, referring to the treaty’s requirements and Mauritius’s status under it. 

In the House of Commons this week, several backbench Labour MPs said they had not previously understood the import of these treaty commitments. “We have only just been made aware of the implications of this African nuclear-weapon-free zone and how it might apply to Diego Garcia,” one MP reportedly said during questions on the floor of the chamber. This admission has intensified cross-party pressure on the Government to halt progression of the treaty ratification until a full security assessment can be presented. Parliamentary records indicate the issue was not clearly discussed in earlier stages of debate on the Bill implementing the Chagos treaty. 

Opposition MPs and some Labour backbenchers argued that Prime Minister Sir Keir Starmer’s government should pause the ratification process immediately, highlighting that both national and allied security may be affected if nuclear deterrent activities and nuclear-capable visits are limited under new treaty obligations.

Conservative peers have already forced a temporary pause in the Chagos Islands legislation in the House of Lords after strong criticism from the United States, where President Donald Trump, who earlier endorsed the deal, has publicly described it as “an act of great stupidity” that could harm Western strategic interests. 

Labour ministers have insisted that existing security provisions in the Chagos treaty and the 99-year lease backing continued use of Diego Garcia by UK and US forces mitigate any risks, and that the Government is committed to ensuring the base’s operational future. Government spokespeople have also downplayed the immediate relevance of the Pelindaba Treaty to day-to-day operations. 

Nevertheless, the debate in Parliament this week highlighted a significant knowledge gap among MPs on a matter that critics say strikes at the heart of Western defence arrangements. Calls to pause the treaty’s ratification have come from across the Commons, with opposition politicians as well as some government backbenchers urging full briefing on all legal and security implications before the agreement is finalised.

As the legislative process continues, the issue of how the Pelindaba Treaty interacts with long-standing UK-US defence cooperation on Diego Garcia is likely to remain a central point of contention in Westminster and in allied capitals.