Diego Garcia Military Base and British Indian Ocean Territory Bill: Reasoned Amendment

MPs voted on 9 September 2025 on a Conservative reasoned amendment to block the Second Reading of the Diego Garcia Military Base and British Indian Ocean Territory Bill. A reasoned amendment is a procedural device that, if passed, would have prevented the Bill from advancing by formally stating the House's reasons for rejecting it at this stage. The amendment was defeated by 333 votes to 116. The Bill implements the treaty signed on 22 May 2025 between the UK and Mauritius, under which Mauritius becomes sovereign over the Chagos Archipelago, including Diego Garcia. In practical terms, the legislation dissolves the British Indian Ocean Territory as a British overseas territory in domestic law, removes it from the British Nationality Act 1981, and grants the UK the right to administer and operate the Diego Garcia military base under Mauritius's authority for 99 years. The vote to defeat the amendment allowed the Bill to proceed to its later stages. The base at Diego Garcia has for decades served as a joint UK-US military facility supporting operations across the Middle East, east Africa and south Asia. The vote divided almost entirely along party lines. All 100 Conservative MPs who voted backed the amendment, joined by all 8 Reform UK MPs, all 5 Democratic Unionist Party MPs, and a handful of independents, giving the Ayes their total of 116. Every Labour, Labour and Co-operative, Green, SDLP, and Your Party MP who voted opposed the amendment, producing the Noes total of 333. No Labour or Labour Co-operative MP voted Aye, and no Conservative MP voted No. The Conservatives' central argument was that the government had capitulated in negotiations and agreed to a financial settlement far beyond what the previous government would have accepted, while the government's response was that the deal as published secures the base's operation and improves on what the Conservatives had been negotiating. With the amendment defeated, the Bill proceeded through its subsequent stages, including a committee sitting on 20 October 2025 where further amendments were considered.