Despite the many controversies it generated, Donald Trump’s state visit to the UK earlier this week was true to form in at least one crucial sense — its ritual celebration of the special relationship — described by the US President as “the greatest alliance the world has ever known”.

But while UK diplomats may have breathed a sigh of relief as these words were uttered, an ongoing international dispute over the fate of an isolated group of islands in the Indian Ocean has left the Anglo-American alliance isolated on the world stage.

In a “crushing” defeat for the UK, last month the United Nations General Assembly overwhelmingly rejected Britain’s claim to continued sovereignty of the Chagos Archipelago in the Indian Ocean. Due to the presence of a major US military base on the largest island in the group, Diego Garcia, the Chagos Islands are a significant lynchpin in the array of defence and security ties that bind Britain and America together.

Despite extensive lobbying, several European allies, including Greece and Spain, voted for the UK to give up its claim to the islands, while others - including France, Germany and the Netherlands - abstained.

At a moment when continued failure to resolve the Brexit crisis has seen the UK’s credibility on the world stage sink to its lowest point for a generation, this setback at the UN represents a further example of how international isolationism on both sides of the Atlantic is eroding Anglo-American global influence.

In 1965, Britain retained control of the Chagos Islands, by carving out the British Indian Ocean Territory from newly decolonised Mauritius in order to fulfil the terms of a backroom deal with American officials. The Pentagon had already marked out Diego Garcia as an optimum site for a major new military base in the region.

For years the story of what happened to the Chagossians – evicted from their island homes through coercion and force by British authorities in the late 1960s – was largely untold. But despite sustained activism from the exile community in the UK, support from various parliamentarians, a favourable High Court ruling in 2000, and the current intensification of the international dispute, the UK government remains intransigent.

Regarded as a mere inconvenience, the Chagossians’ struggle to return is an uncomfortable reminder to the powerful of what happens to those who fall through the cracks of grand geopolitical schemes.

These schemes don’t come much grander than the creation of Naval Support Facility Diego Garcia. Since its construction, the base has been a vital link in the global network of geographically isolated installations that maintain global US military hegemony.

The base has been a crucial node in controversial operations, such as the ‘shock and awe’ bombing campaigns during the 2003 invasion of Iraq, and as a black site for extraordinary rendition flights – which saw the US outsource detention and interrogation to some of the world’s most brutal regimes.

With British politicians mapping out a fantasy vision of “Empire 2.0” - in which the country’s old colonial ties will be revived to replace those being severed with the European continent - one glaring reality becomes apparent. Britain has yet to come to terms with its imperial legacy.

Indeed, as the case of the Chagos Islands demonstrates, the idea of a new trading empire to be forged by this new “global Britain,” ignores the extent to which colonial attitudes still inform how the UK operates.

In 2009, Colin Roberts, then Governor of the BIOT, noted that establishing a marine park around the Chagos Islands would ensure that "there will be no human footprints nor Man Fridays on these uninhabited islands". The reference to Man Friday, the native servant in Daniel Defoe’s 18th-century novel Robinson Crusoe, shows a blatant disregard for the Chagossians claims. But UK officials have also expressed these attitudes in troubling ways through their treatment of the exiled community.

Britain has consistently denied the community a right of return, and has also pursued policies that have left some in a strange limbo, imposing a kind of double homelessness.

Lawyers acting in the interests of third generation Chagossians, now denied British citizenship, have likened the situation to the Windrush Scandal: Chagossians who have been raised in the UK, they contend, are now subjected to a ‘hostile environment,’ and deported when they turn 18.

The wider struggle of the 3,000 strong Chagossian community now residing in England, mostly based in Crawley near Gatwick Airport, is documented in Another Paradise, a new feature-length film which premieres at Sheffield Doc/Fest this Saturday.

The film’s director, Olivier Magis, places the fundamental hypocrisy of the UK government’s attitude to the Chagossian community at the heart of his project:

“At a time when thousands of people are risking their lives to reach European shores, the Chagossians beg the United Kingdom to let them go home. These people are asking to no longer be migrants, yet their plea is systematically rejected. In a country where pro-Brexit rhetoric is partly built by encouraging fear of immigrants, this attitude towards the Chagossians is Kafkaesque and incomprehensible.”

Thus far, the UK government is ignoring international pressure, and continuing to assert its sovereignty, citing “feasibility, defence and security interests, and the cost to the British taxpayer” to justify its decision to rule out resettlement of the islands. In its response to the UN General Assembly, it strongly denied claims by Mauritius that the forced removal of the island's population by British military forces amounted to a crime Against humanity.

When the live wire of the legacy of colonialism comes into contact with the brutal realities of a UK gripped by a wider existential crisis about its role in the world, there is an overwhelming desire amongst those in power to simply forget.

Although the exiled Chagossian community continues to practice its island culture, time is running out: when the generation of elders who can still remember life on the islands fade, they will take those memories and that lived culture with them.

“It’s time to kill Goliath,” says the coach of the Chagos Islands football team, whose unsuccessful campaign at an international football tournament for stateless peoples features prominently in Another Paradise.

It’s hard to think of a more uneven struggle than that of a few thousand impoverished exiles, standing up against the interests of two members of the UN Security Council. But for the Chagossians, this isn’t simply a fight to put right past wrongs — it is a battle for survival.

The world premiere of Another Paradise takes place on Saturday 08 June at Sheffield Doc Fest. Sabrina Jean, the film’s key participant, and filmmaker Olivier Magis will be in attendance.