The UK government is working with Mauritius to finalise a deal on the future of the Chagos Islands, Downing Street has said.

Under the proposed agreement, Mauritius would gain sovereignty of the islands from the UK, but would allow the US and UK to continue operating a military base on one of the islands for an initial period of 99 years, at a cost to the British taxpayer.

UK government sources have indicated they are not waiting for further sign-off from Donald Trump.

Earlier this year, Foreign Secretary David Lammy said the deal would not go ahead if the US president had objections.

In a statement, the Mauritian government reiterated Downing Street's comments, saying that both countries were "currently working to finalise this agreement".

The plan to hand over control of the Chagos Islands, officially known as the British Indian Ocean Territory, was announced last October following negotiations with then-Mauritian leader Pravind Jugnauth.

However, following the elections, he was replaced by the current PM, Navin Ramgoolam, who expressed concerns about the deal.

Progress on reaching agreement was also delayed after the election of Trump because negotiators wanted to give the new US administration time to examine the details of the plan.

Reform UK leader - and Trump ally - Nigel Farage had suggested that the proposal would be met with "outright hostility" by the new US president's team.

In October, the US Secretary of State Marco Rubio said the deal posed a "serious threat" to US national security, citing Mauritius' relationship with China.

However, last month Trump indicated he would back the deal.

Asked about it at a press conference with Prime Minister Sir Keir Starmer in the Oval Office last month, he said: "We're going to have some discussions about that very soon, and I have a feeling it's going to work out very well.

"They're talking about a very long-term, powerful lease, a very strong lease, about 140 years actually.

"That's a long time, and I think we'll be inclined to go along with your country."

The Chagos plan is expected to enable the UK to lease Diego Garcia for 99 years. Ramgoolam has previously said the deal included a clause allowing for a further 40 year-extension.

The Conservatives have fiercely criticised the deal, with party leader Kemi Badenoch arguing it was "not in our national interest to give [them] away and pay for the privilege of doing so".

There have been reports that deal could cost the UK government up to £18bn, a figure the Foreign Office has labelled "inaccurate and misleading".

The government has not yet said how much the deal would cost but Sir Keir has promised to inform MPs of the details once the agreement is finalised.

He defended the deal, calling it "extremely important for our security".

The Chagos Archipelago was separated from Mauritius in 1965, when Mauritius was still a British colony.

Britain purchased the islands for £3m, but Mauritius has argued that it was illegally forced to give away the Chagos Islands as part of a deal to get independence from Britain.

In the late 1960s Britain invited the US to build a military base on Diego Garcia and removed thousands of people from their homes on the island.

In recent years, the UK has come under growing international pressure to return the islands to Mauritius, with both the United Nations' top court and general assembly siding with Mauritius over sovereignty claims.

In late 2022, the previous Conservative government began negotiations over control of the territorybut did not reach an agreement by the time it lost power in the 2024 general election.