The UK will hand over sovereignty of the remote Chagos Islands to Mauritius after a decades-long dispute.

The deal to transfer the Indian Ocean archipelago to Mauritius includes the tropical atoll of Diego Garcia, home to a military base used by the UK and the US that plays a crucial role in the region’s stability and international security.

Under the agreement, the base will remain under UK and US jurisdiction for at least the next 99 years.

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The UK government said that the treaty would “address wrongs of the past and demonstrate the commitment of both parties to support the welfare” of Chagossians – the native people of the islands.

Several leading Conservatives have called the decision “weak”, with former securities minister Tom Tugendhat saying it is a “shameful retreat undermining our security and leaving our allies exposed”.

Since 1971, only Diego Garcia has been allowed inhabitants – US military employees – after the UK expelled the Chagossians at the request of the US. Some moved to Mauritius and some have lived in the UK, in Crawley, West Sussex, since 2002.

About 89 Sri Lankan Tamil asylum seekers arrived on Diego Garcia in 2021 but the UK government has argued the refugee convention does not apply there so they remain in limbo.

Mauritius has been trying to claim the Chagos Islands back from the UK since the French handed them over in 1845.

A statement from the Mauritian and UK governments said Mauritius is now “free to implement a programme of resettlement” on the islands, other than Diego Garcia, and the UK will provide money and other support to Chagossians who had to leave.

The UK will also provide a “package of financial support” to Mauritius, including annual payments for the next 99 years and will provide funding for an infrastructure partnership.

Foreign Secretary David Lammy said: “This government inherited a situation where the long-term, secure operation of the Diego Garcia military base was under threat, with contested sovereignty and ongoing legal challenges.

“Today’s agreement secures this vital military base for the future.

“It will strengthen our role in safeguarding global security, shut down any possibility of the Indian Ocean being used as a dangerous illegal migration route to the UK, as well as guaranteeing our long-term relationship with Mauritius, a close Commonwealth partner.”

US President Joe Biden welcomed the move, saying: “I applaud the historic agreement.

“It is a clear demonstration that through diplomacy and partnership, countries can overcome long-standing historical challenges to reach peaceful and mutually beneficial outcomes.”

The agreement is subject to the finalisation of a treaty and supporting legal instruments, with both Mauritius and the UK committing to complete “as quickly as possible”.