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Donald Trump called the deal a 'great act of stupidity' despite previously supporting the Chagos agreement

Andy Burnham is set to face a brutal Chagos showdown in the UN's next General Assembly meeting as Mauritius has begun piling on the pressure.

The Prime Minister plans to attend the annual gathering in New York, marking his first international summit since taking office.

However, the trip risks being overshadowed by renewed pressure from Mauritius over Britain's stalled sovereignty agreement.

The UK signed a deal in May 2025 to hand the Chagos Islands to Mauritius, alongside billions of pounds in payments to lease back the Diego Garcia military base.

The agreement had initial backing from the White House, but has stalled since April when US President Donald Trump withdrew his support.

Mr Trump described the transfer at the time as an "act of great stupidity".

Legislation needed to implement the deal was subsequently dropped by the Government and ministers have not yet indicated whether it will be revived.

Mr Burnham now finds himself in a difficult position - unable to proceed without angering Washington, yet equally unable to abandon the deal for fear of legal action from Mauritius.

Sources within the Mauritian government told The Telegraph officials intend to use the UN summit to increase pressure on Mr Burnham to honour the agreement.

Mauritius is currently facing an unfunded budget deficit of £170million, which it had hoped to offset via rental payments from the UK for the Diego Garcia lease and wider consolation over its 1965 "colonisation".

One official in the Mauritian capital, Port Louis, said "all possibilities were being looked into" as the country weighs up its options heading into the summit.

One option being considered is sanctioning the UK for not upholding the deal, which could disrupt the military base's ability to operate communications systems, receive mail or handle aircraft.

The Mauritian Government could also seek a UN resolution declaring Britain's continued presence on the island is unlawful or refer the matter to the International Court of Justice (ICJ).

The ICJ previously ruled in 2019 the islands should be handed to Mauritius.

Any such moves would not force an immediate handover of the land, but would apply diplomatic pressure on the UK.

Mauritius could also challenge Britain's broader reputation as an upholder of international law.

Mauritius has previously secured backing on the issue from the African Union, which frames the dispute as a matter of decolonisation.

It has also received support from the Alliance of Small Island States, a coalition representing 39 small island nations.

Speaking in Ukraine on Monday, Mr Burnham indicated he was likely to attend the UN summit, though final details had not been confirmed.

He said: "I've not fully confirmed the details yet, but it's likely I will go, particularly after today's discussion. Leaving today, I'm quite clear what I need to do in the next few weeks."

The visit could also include Mr Burnham's first face-to-face meeting with President Trump.

However, he is unlikely to attend the summit himself but could host the Prime Minister afterwards at the White House.

The Chagos dispute previously strained relations between Mr Trump and former Prime Minister Sir Keir Starmer, after the UK declined to let the US use British bases, including Diego Garcia, for offensive strikes on Iran.

Mr Trump had originally supported the UK-Mauritius agreement, which involves Britain relinquishing sovereignty in exchange for a 99-year lease on the base.

His position shifted following the dispute over base access, prompting him to claim he had warned Sir Keir against entering a "100-year lease".

Under the agreement, the UK committed to paying Mauritius £35billion over the course of the lease, which the previous Labour government said equated to roughly £101million a year once inflation and Treasury discounting models were applied.

Jonathan Powell, the No10 security adviser originally appointed by Sir Keir to handle the Chagos negotiations, has remained in post under Mr Burnham.

A spokesman for the Foreign Office said: "Diego Garcia is a key strategic military asset for both the UK and the US, which has protected our shared security for nearly 60 years.

"This Government inherited a situation where UK control over the vital military base on Diego Garcia was under threat. Maintaining long-term operational control and security of Diego Garcia is the entire basis for the UK-Mauritius Agreement.

"We will continue to work closely with the US and Mauritius on the way forward that is in the UK's best interests and protects our national security."