Lancaster House Agreement

The 1965 agreement under which Mauritius accepted compensation and arrangements concerning the Chagos Islands before independence. It provided for the archipelago’s separation from Mauritius and its retention under British sovereignty.

Chagos Archipelago: An Indian Ocean island group separated from Mauritius in 1965 and retained under British sovereignty. The agreement addressed the archipelago’s separation and future use.
Mauritius: An island country in the Indian Ocean that became independent from Britain in 1968. Its colonial government negotiated the agreement before independence.
Chagos sovereignty dispute: The dispute over whether sovereignty over the Chagos Archipelago belongs to Mauritius or the United Kingdom. Mauritius has challenged the separation formalized alongside the agreement.
Mauritius–United Kingdom agreement on the Chagos Archipelago: A 2025 agreement providing for Mauritius to gain sovereignty over the Chagos Archipelago while Diego Garcia remains available for military use. It revisits the sovereignty and defense arrangements set out in 1965.
British Indian Ocean Territory: A British overseas territory established in 1965 from the Chagos Archipelago. The agreement’s separation arrangements enabled Britain to create this territory.
British Empire: A global empire governed by Britain through colonies, dominions, and other territories. The agreement was made during Britain’s withdrawal from colonial rule.
International Court of Justice advisory opinion on the Chagos Archipelago: A 2019 advisory opinion finding that Britain’s decolonization of Mauritius was not lawfully completed. The Court examined the separation of Chagos in the context of Mauritius’s independence.
International Tribunal for the Law of the Sea Chagos arbitration: A 2015 arbitration concerning Mauritius’s maritime rights and Britain’s establishment of a marine protected area around Chagos. The tribunal addressed legal consequences of Britain’s administration after the agreement.
Mauritian independence: Mauritius’s transition from British colonial rule to sovereignty in 1968. The agreement linked Chagos arrangements and compensation to independence.
Harold Wilson: British prime minister from 1964 to 1970 and from 1974 to 1976. His government conducted the negotiations that produced the agreement.

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