The Telegraph reports that the Prime Minister was referred to the ICC by a group of indigenous people from the Islands on Monday.
In May, the UK Government signed a £3.4 billion deal to hand over sovereignty of the Chagos Islands to Mauritius.
The UK will still retain control of a UK-UK military base on one of the largest islands, Diego Garcia.
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The 99-year agreement has been criticised by Chagossians now resident in the UK.
And now campaigners have accused Starmer, former foreign secretary David Lammy and Defence Secretary John Healey of continuing the “deportation or forcible transfer of population” by refusing to allow native people to return to Diego Garcia.
The Chagos Islands were retained by the UK as an overseas territory when Mauritius won its independence in 1968.
The Diego Garcia base was constructed in the 1970s, and the UK has been accused of breaking international law by deporting islanders to allow this to happen.
Now, campaigners have claimed that Starmer has continued the displacement because the Chagos deal will not allow them to return to Diego Garcia when Mauritius takes over ownership later in the year.
The referral to the ICC, the Telegraph reports, calls the displacement of Chagossians “one of the longest-standing and most egregious cases of displacement in modern history”.
It claims Starmer, Lammy, and Healey have “knowingly perpetuated crimes against humanity” by failing to allow displaced people to return to the islands.
Victims have “waited half a century for justice”, it adds.
Parliament is due to debate the treaty on Tuesday.
Bertrice Pompe, who was born on Diego Garcia, is leading the push to stop the deal going through. She previously secured an interim injunction stopping the UK and Mauritius from signing the treaty, hours before it was due to be announced.
It was later overturned, and the deal went through.
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Campaigners say that the Chagos deal allows Mauritius to implement a “programme of resettlement” for displaced islanders, it is “merely optional”.
“We are pleading with all those who have the power to make a difference to please step in and stop these crimes against humanity,” Pompe said.
“We are the indigenous of the Chagos Islands, we bear their name, and we need our voices to be heard.”
Campaigners also published an open letter to ICC prosecutor Karim Khan, urging him to open a crimes against humanity case against Starmer.
“While it may be difficult or impossible to investigate the original perpetrators from the 1960s and 1970s, it is both possible and necessary to investigate those who now perpetuate the crime,” the letter reads.
“By signing and promoting the 22 May 2025 Agreement, the Prime Minister has knowingly entrenched deportation, persecution and other inhumane acts.”
In regards to Lammy and Healey, the letter adds: “The Foreign Secretary negotiated the Agreement that excludes us”, while “the Defence Secretary has justified our exclusion on strategic grounds”.
It is now up to the ICC to decide whether or not to open a preliminary investigation into the UK Government’s handling of the Chagos deal.
If the court decides there is a case to answer from ministers, it could then proceed to a full investigation for crimes against humanity.
