Human Rights Watch (HRW) said reparations should be paid to generations of people affected by the decision to depopulate the remote islands, deep in the Indian Ocean.

The UK's Foreign Office has responded by repeating its “deep regret” about the manner in which people were removed from the islands in the late 1960s and early 70s. But it stressed that “we categorically reject the characterisation of events” as crimes against humanity.

The HRW report comes as the UK is facing growing international condemnation for holding on to what it calls the “British Indian Ocean Territory,” with the UN’s International Court of Justice ruling that the continuing British occupation of the archipelago is illegal. 

The UN General Assembly has also voted, overwhelmingly, in favour of the islands being returned to Mauritius.

“The UK is today committing an appalling colonial crime, treating all Chagossians as a people without rights. The UK and the US, who together expelled the Chagossians from their homes, should provide full reparations for the harm they have caused,” said HRW’s senior legal adviser, Clive Baldwin.

The UK insisted on keeping hold of the Chagos islands when it negotiated Mauritius’s independence in 1968. Mauritian officials have since accused the UK of “blackmailing” them into relinquishing the territory. 

The UK had already entered into secret talks with the US to lease one of the islands, Diego Garcia, to Washington for use as a military base.

Today the Foreign Office insisted that base “helps to keep people in Britain, the region and around the world safe, combatting some of the most challenging threats to international peace and security, including those from terrorism and piracy, and responding to humanitarian crises".

But with all but a handful of nations now backing Mauritius’s claim, the UK has now entered into negotiations about the sovereignty of the Chagos archipelago. 

Jagdish Koonjul, Mauritius’s UN ambassador, described those talks as “constructive", and his government welcomed the HRW report, saying: “Justice must be done.” 

Mauritius insists the US can continue to keep its base on Diego Garcia, and that it will commit to resettling “any individuals of Chagossian origin” on their home islands.