Keir Starmer was accused of a ‘shameful retreat’ yesterday over the strategic Chagos Islands

Diego Garcia, the largest island in the Chagos archipelago and site of a major United States military base in the middle of the Indian Ocean leased from Britain

An aerial view of the air operations area and runway at the Diego Garcia base

Chinese President Xi Jinping waves as he arrives for a press event on October 23, 2022

He added: ‘This is a huge mistake – a fatal mistake. We’re the worst country in the world for understanding our strategic arrangements – make no mistake, the free world will be in danger.’

Tory leadership contender Robert Jenrick added: ‘It’s taken three months for Starmer to surrender Britain’s strategic interests.

‘This is a dangerous capitulation that will hand our territory to an ally of Beijing.’

Fellow hopeful Tom Tugendhat said: ‘That [agreement] covers Diego Garcia. What about the other islands? Mauritius is free to rent them out to anybody else including, for example, China.

‘This deal not only threatens our security but also undermines our allies, opening the possibility of China gaining a military foothold in the Indian Ocean.’

The Times reported last night that Sir Keir renounced sovereignty of the Chagos Islands despite private warnings from the United States.

Over the summer, Washington asked Britain what it would take to reconsider, but the Foreign Office said it did not recognise the ‘characterisation’ of those discussions as private warnings.

The islands, also known as the British Indian Ocean Territory, have long been cherished by the UK because of the sprawling and secretive military base on Diego Garcia, which has refuelled Western bombers involved in tackling the Taliban in the Middle East.

Following the eviction of the native population (Chagossians) in the 1960s, the only inhabitants are US and British military personnel

The United Nations’ highest court, the International Court of Justice (ICJ), ruled in 2019 that the UK’s administration of the territory was ‘unlawful’ and must end, after Mauritius said it was illegally forced to give up the islands to secure its own independence from the UK in the 1960s.

But after years of ignoring the ‘advisory opinion’, in 2022 then-foreign secretary James Cleverly announced a major reversal in policy by opening up negotiations, with hopes of a settlement within months.

As Mr Cleverly decried Labour as ‘weak’ and accused the party of lying when it ‘said that they’d be patriotic’, Mr Tugendhat aimed a dig at his leadership rival, saying: ‘This is a shameful retreat undermining our security and leaving our allies exposed… it was disgraceful that these negotiations started under our watch.’

Jonathan Powell, the Prime Minister’s special envoy for negotiations between the UK and Mauritius, said Sir Keir met the Mauritian prime minister in July, shortly after Labour swept to a landslide election victory, with a view to getting the deal agreed swiftly.

Yesterday members of the Chagossian community settled in Britain accused Labour of being ignorant of history.

Maxwell Evenor said he found life extremely difficult in Mauritius as a Chagossian and moved to the UK in 2010 with his family.

‘This is history repeating itself,’ he said. ‘The Chagossians do not have a voice and they will never have a voice under the Mauritian flag. This is just injustice.’

Around 1,000 islanders were forced to leave Chagos by 1973 to make way for the Diego Garcia base.

Many settled in the commuter town of Crawley in West Sussex and have spent decades fighting to return to the islands.

It would be for the Mauritian government to decide whether any of the islanders displaced more than half a century ago could return to Chagos.

Frankie Bontemps (centre) with members of the Chaggosian community in Crawley

The British Indian Ocean Territory (BIOT) or Chagos Islands (formerly the Oil Islands) is an overseas territory of the United Kingdom situated in the Indian Ocean

Former defence secretary Grant Shapps said the situation was ‘absolutely appalling’, adding: ‘Surrendering sovereignty here creates read across to other British bases. It’s a weak and deeply regrettable act from this government.

‘Yesterday’s decision will ease international pressure on the UK to honour the ICJ advice.’

But Professor Richard Ekins, of the Policy Exchange think-tank, said: ‘The UK is under no legal or moral obligation to cede the Chagos Islands to Mauritius and should not be intimidated into doing so, at significant cost to vital strategic interests, by the abuse of the International Court of Justice’s advisory jurisdiction.

‘US President Joe Biden welcomed the ‘historic’ agreement and said it secured the ‘effective operation of the joint facility on Diego Garcia into the next century’.

Foreign Secretary David Lammy said: ‘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.’

A Downing Street spokesman said Sir Keir spoke to his Mauritius counterpart, Pravind Jugnauth, yesterday morning, adding: ‘The Prime Minister reiterated the importance of reaching this deal to protect the continued operation of the UK/US military base on Diego Garcia.’

A Labour source said last night: ‘Labour inherited a legal car crash that could have left this vital military base in the hands of the court, damaging UK and US national security.

‘The new Government did the deal to secure the base and shut off a potential illegal migration route.’