Alarm has been sounded warning Labour's new £6million plan will give migrants backdoor access to Britain.
Author and vet Joe Hollins has been resident on St Helena, a British Overseas Territory (BOT), since 2009. He warned: "Correctly or incorrectly, this will now present the opportunity of a gateway into Europe."
The Government announced its decision to relinquish sovereignty on the Chagos Islands earlier this month, which they have argued "saved" a UK-US military base on Diego Garcia, which is part of the archipelago.
A further deal was then made with St Helena that any migrants that may arrive on the Chagos Islands in the interim period before the deal with Mauritius is finalised, would be sent to St Helena to have their asylum applications processed.
Any such migrants are now set to have their asylum applications decided by St Helena, an island 5,000 miles away from the Chagos Islands, and in return the UK will provide St Helena with £6m in funding to improve health and education outcomes, and upgrade government infrastructure.
St Helena, part of the South Atlantic British possessions of Saint Helena, Ascension and Tristan da Cunha, has a history steeped in migration with people from all over the world making up its genetic heritage.
As it was a former resupply stop for maritime traffic for more than 200 years, the South Atlantic island became home to many different people, including the French Emperor Napoleon, who died there after being banished by the British.
Speaking about the potential arrival of a new wave of migrants to St Helena, Mr Hollins, who penned Vet at the End of the Earth: Adventures with Animals in the South Atlantic, said: "The publicity accorded to this deal will not have gone unnoticed in relevant nations that may act as a source for migration to the Chagos Islands such as Sri Lanka, where the economy has tanked and poverty is on the climb.
"Correctly or incorrectly, this will now present the opportunity of a gateway into Europe.
"It is one thing for economic and political migrants to attempt to reach the Chagos Islands and request asylum, knowing, from the fate of the 60 Sri Lankan migrants trapped on Diego Garcia, that prospects are limited.
"It is another now knowing that they will be airlifted to St Helena at UK government expense, with better prospects for lifestyle, family and ultimately, work and even possibly British citizenship.
"This gateway has essentially been internationally advertised and must surely be a highly attractive opportunity, so I find the oft flogged quote that there have been no migrants (to the Chagos Islands) since 2022 a tad disingenuous."
Mr Hollins added that there could be some benefits to St Helena from renewed immigration as the population had "ebbed away from nearly 10,000 in the early 1900s to just over 4,000 in the present day".
He continued: "There is an argument that a population injection of incentivised newcomers could be beneficial to the island economy.
"It is also a temporary arrangement until the agreement to hand over the islands to Mauritius has been fully ratified and does not currently include migrants who are already there, so there appears to be a failsafe.
"On the plus side, we can’t ignore the fact that of the ten inhabited overseas territories, St Helena is one of only four (St Helena, Tristan da Cunha, Pitcairn and Montserrat) that draw on the UK overseas aid budget for funding.
"The UK currently meets around 60% of our budgetary needs, equivalent to £6,000 to £8,000 per head of population (2021), and so £6.5 million can’t be sniffed at."
Labour Foreign Office minister Stephen Doughty said migrant deal was an "interim contingency solution" before Mauritius takes control of the Chagos Islands.
However, in the Commons this week Shadow foreign secretary Andrew Mitchell had raised concerns that "an influx of migrants could adversely impact what is a very tight-knit local community" in St Helena, adding: "What is the estimated number of migrants that will be sent to St Helena?
He said: "Bearing in mind that the entire population is less than 5,000, will he be imposing - an admittedly low - but nevertheless, a limit?"
Labour Foreign Office minister Stephen Doughty said migrant deal was an "interim contingency solution" before Mauritius takes control of the Chagos Islands.
However, in the Commons this week Shadow foreign secretary Andrew Mitchell had raised concerns that "an influx of migrants could adversely impact what is a very tight-knit local community" in St Helena, adding: "What is the estimated number of migrants that will be sent to St Helena?
He said: "Bearing in mind that the entire population is less than 5,000, will he be imposing - an admittedly low - but nevertheless, a limit?"