The United Kingdom has been found in breach of international law in retaining control of the Chagos Islands in the Indian Ocean, and told it must return them to Mauritius as quickly as possible, by the International Court of Justice in an advisory opinion.

By 13 votes to one, the court held that the process of decolonisation of Mauritius was not lawfully completed on its independence in 1968, when the UK separated the islands from Muaritius and incorporated them into the British Indian Ocean Territory (BIOT), in order that the United States could build a military base on Diego Garcia. About 2,000 islanders were evicted in the process.

Both the islanders and Mauritius have brought proceedings in the UK courts as well as before the ICJ to restore their rights in the islands, but yesterday's ruling is their first victory.

In its decision the court said that the peoples of non-self-governing territories were entitled to exercise their right to self-determination in relation to their territory as a whole, the integrity of which must be respected by the administering power. "It follows that any detachment by the administering power of part of a non-self-governing territory, unless based on the freely expressed and genuine will of the people of the territory concerned, is contrary to the right to self-determination."

Having regard to the circumstances in which the colony of Mauritius agreed in principle to detachment of the islands, the court considers that this was "not based on the free and genuine expression of the will of the people concerned". It concluded that, as a result of the archipelago’s unlawful detachment and its incorporation into the BIOT, "the process of decolonisation of Mauritius was not lawfully completed when Mauritius acceded to independence in 1968".

In consequence, the UK's continued administration "constitutes a wrongful act entailing the international responsibility of that state... the United Kingdom has an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible, and... all member states must co-operate with the United Nations to complete the decolonisation of Mauritius".

As regards the resettlement of the islanders, "this is an issue relating to the protection of the human rights of those concerned, which should be addressed by the General Assembly during the completion of the decolonisation of Mauritius".

Click here for the press release summary, and here for the opinion.