A decision was made in the case of the international boundary dispute over the Chagos Islands, which had been referred to the International Court after an overwhelming UN General Assembly vote in 2017.

In the opening submissions of the legal challenge, Sir Anerood Jugnauth, Mauritius’s Minister of Defence, alleged that his country had been coerced into giving up a large swathe of its territory before independence. This was in breach of UN Resolution 1514, passed in 1960, which banned the separation of colonies before independence.

Jugnauth is reported to have told the court in 2018, “I am the only one still alive among those who participated in the Mauritius Constitutional Conference at Lancaster House [in London] in 1965, where talks on the ultimate status of Mauritius were held.” Those talks resulted in “the unlawful detachment of an integral part of our territory on the eve of our independence,” he said.

“These secret meetings were not, at that time, made known to the other Mauritian representatives, myself included, although we were later told of the immense pressure that was imposed on the small group.”

Mauritius’s presentation included a video statement by an exiled Chagossian, Marie Liseby Elysé, who was forcibly evicted from the islands in 1973. “We were like animals and slaves in that ship. People were dying of sadness,” she said.

Prof Philippe Sands QC, representing Mauritius, told the International Court of Justice: “No country wishes to be a colony. The mere possibility engenders strong feelings… The right to self-determination is not a ‘heritage’ issue. This is not Africa in the late 19th or early 20th century. This is September 2018.”

Robert Buckland QC, who appeared on behalf of the UK, only acknowledged the disenfranchisement of Chagossions and not the issue of sovereignty. He said the UK “accepts that the way Chagossions were treated was shameful and wrong and deeply regrets that fact”.

Read: The lost continent of “Mauritia” is submerged under the Island of Mauritius

UK’s sovereignty over the Chagos Islands rejected

The UK’s continued possession of the Chagos archipelago saw it being classified as “British Indian Ocean Territory”, or “BIOT”. The UK went on to lease the biggest island, Diego Garcia, to the United States of America, which established its largest overseas military air base there. This was at the expense of about 1 500 native islanders who were deported to make room for the US air base.

The Guardian newspaper reported that the President of the International Court of Justice, Abdulqawi Ahmed Yusuf, said the process of separating the Chagos Islands from Mauritius during decolonisation in the 1960s constituted an “unlawful detachment” and was a “wrongful act”.

While delivering the judgment he said the detachment of the Chagos archipelago in 1965 from Mauritius had not been based on a “free and genuine expression of the people concerned”.

“This continued administration constitutes a wrongful act,” he added. “The UK 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.”

Welcoming the ruling, the Mauritian government said it was a “historic moment in efforts to bring colonialism to an end and to promote human rights, self-determination and the international rule of law”.

Jugnauth added, “This is a historic moment for Mauritius and all its people, including the Chagossians who were unconscionably removed from their homeland and prevented from returning for the last half century. Our territorial integrity will now be made complete, and when that occurs, the Chagossians and their descendants will finally be able to return home.”

Prof Sands QC advised caution: “It’s difficult to imagine the UK, as it moves forward into this Brexit world, ignoring what the International Court of Justice and the UN General Assembly have said. The UK is a country that prides itself on respect for the rule of law. Our hope and expectation is that the UK will honour the ICJ’s findings and give effect to it as rapidly as possible.”

This verdict and the UN General Assembly’s 2017 vote, which followed the Brexit referendum, show that the UK’s international influence is steadily waning.