The Chagos Islands is being unlawfully occupied by the United Kingdom, the International Court of Justice (ICJ) ruled on Monday.

The court said the UK should now cede control of its last African colony. “It is an unlawful act of a continuing character,” the court said.

Chief judge Abdulqawi Ahmed Yusuf added: “The United Kingdom is under an obligation to bring an end to its administration of the Chagos Archipelago as rapidly as possible, thereby allowing Mauritius to complete the decolonisation of its territory.”

The ruling of the International Court of Justice (ICJ), the United Nations’ highest court, is not binding.

It is an advisory opinion sought by the UN General Assembly. Nonetheless, the ruling carries symbolic weight — although that may not be enough to force Britain’s hand, given the Chagos Islands’ immense geostrategic importance and the American military base which is hosted there.

The Chagos Islands were officially part of Mauritius when that island nation achieved its independence in 1968. But Britain unilaterally annexed the Chagos Islands because of their immense geostrategic value. The islands are ideally positioned in the middle of the Indian Ocean, and the United States has operated a military base there since the late 1960s — paying Britain only a minimal rent to do so. That lease runs until the 1930s.

To make way for the military base, the United Kingdom forcibly removed all Chagos Islanders from their home. Many were shipped in squalid conditions to Mauritius, where they were dumped with no support. Some who resisted their removal had their pet dogs gassed to death by British agents as a warning.

Last year, the British government threatened to deport the descendants of Chagos Islanders who had made it to Britain, as part of Prime Minister Theresa May’s infamous ‘hostile environment’ policy, which is designed to make life in the UK as difficult as possible for immigrants.

In theory, the ICJ ruling paves the way for Mauritius to take control of the islands. Its claim of sovereignty is supported by the African Union and 17 other nations, including: Mauritius, which argues that the Chagos Islands should fall under its sovereignty.

Seventeen other nations support Mauritius’ claim of sovereignty: Belize, Botswana, Brazil, Cyprus, Germany, Guatemala, India, Kenya, the Marshall Islands, Mauritius, Nicaragua, Nigeria, Serbia, South Africa, Thailand, Vanuatu and Zambia.

But Chagos Islanders themselves are not so sure that Mauritius is necessarily a better option. As the Mail & Guardian reported in September last year, while the community broadly rejects continued British hegemony, many are equally uncertain about the prospect of being ruled by Mauritius, who could turn out to be just a different style of colonial power.

“No one did approach us as a community to ask what we want. We don’t know what Mauritius is going to do. They say they will resettle us back but the base is still going to be there, they don’t mind about that, and the Americans don’t want us there, so there are contradictions in that,” Isabel Charlot, the chairperson of the Chagos Islanders Movement, whose father was born on Chagos.

She was concerned that that Mauritius intends to develop the islands for its own benefit, and that its promises to resettle islanders are insincere.

The ICJ ruling has not allayed those concerns, Charlot said. “We did believe that today it would have been about the Chagossians. We did hope that the judges would have used their wisdom and knowledge to safeguard the best interests of the Chagossians…for once it would have been about us but it was political.”Isabel Charlot, whose father was born on Chagos told media. She is concerned that that Mauritius intends to develop the islands for its own benefit, and that its promises to resettle islanders are insincere.

Timothy Walker, a maritime security expert with the Institute for Security Studies, said that the ICJ ruling represents a serious blow for Britain’s foreign policy. “The UK’s standing in international relations has already been undergoing a huge amount of criticism and pressure in the last couple of years, and this will add to it in a dimension which is now becoming one of the most important in the world — sovereignty over maritime territory.”