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British Indian Ocean Territory: Sovereignty

Question for Foreign and Commonwealth Office

UIN 117, tabled on 14 October 2019

To ask the Secretary of State for Foreign and Commonwealth Affairs, which international legally binding agreements enshrine UK sovereignty over the British Indian Ocean Territory.

Answered on

17 October 2019

​We have no doubt about our sovereignty over the British Indian Ocean Territory (BIOT), which has been under continuous British sovereignty since 1814. The 1965 United Kingdom – Mauritian Lancaster House Agreement was a freely negotiated package that expressed the consent of Mauritius to the detachment of the Chagos Archipelago in return for certain benefits, including a sum of £3 million and a United Kingdom commitment to cede the territory to Mauritius when it is no longer needed for defence purposes. Internationally, Mauritian Ministers reaffirmed the 1965 Agreement on several occasions, at the highest level. The 1965 agreement was held to be legally binding by a UN Convention on the Law of the Sea (UNCLOS) arbitral tribunal in 2015.

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