LONDON — Sri Lankan Tamil migrants were unlawfully detained for years on the remote British territory of Diego Garcia, a judge has ruled.

In 2021, dozens of Tamils became the first people ever to claim asylum on the Indian Ocean island, which is the site of a secretive UK-US military base.

They were held for years in a small fenced-off camp, before being brought to the UK earlier this month in what the government described as a "one-off" move in the interests of their welfare.

A spokesperson for the UK government said it was "carefully considering" Monday's judgment.

Diego Garcia was never a "suitable long-term location for migrants" and the government "inherited a deeply troubling situation that remained unresolved under the last administration for years", the spokesperson added.

Lawyer Simon Robinson with UK firm Duncan Lewis, which is representing some of the migrants, said "questions need to be answered about how, in the 21st century, this was able to happen".

The ruling follows a landmark hearing held in a converted chapel on the island in September. The BBC gained unprecedented access to the island and the migrant camp there to cover the proceedings.

Diego Garcia is part of the Chagos Islands, or British Indian Ocean Territory (Biot), an area described as being "constitutionally distinct" from the UK. It is administered from London by a commissioner based out of the Foreign Office.

In their time on the island, the Tamils, including 16 children, were housed in military tents in the fenced camp, which was guarded at all times by private security company G4S.

Tamils have described their time on the island as like living in "hell".

"It's like an open prison - we were not allowed to go outside, we were just living in a fence and in a tent," one woman told the BBC after being brought to the UK with her husband and two children this month.

During a site visit to the camp in September, the court saw rips in some of the tents and rats nesting above military cots that the migrants were given as beds.

There were multiple hunger strikes and numerous incidents of self-harm and suicide attempts in response to the conditions in the camp, after which some people were transferred to Rwanda for medical treatment.

There were also cases and allegations of sexual assault and harassment within the camp by other migrants, including against children.

Margaret Obi, acting judge of the Biot supreme court, said in her ruling on Monday that the camp was a prison "in all but name" and "had been a prison from the outset".

She found that one former deputy commissioner "appeared to have only a limited appreciation of the fundamental importance of liberty".

Tom Short, a lawyer with firm Leigh Day, said the judgement was "not only a vindication of our clients' rights but a triumph for the rule of law in the British Overseas Territories."

"Such an affront to fundamental rights should never have happened and in due course this travesty of administration must be looked at in full," he added.

The camp has now closed but two men with criminal convictions and another under investigation remain on Diego Garcia, the BBC understands.

Britain took control of the Chagos Islands from its then colony, Mauritius, in 1965 and went on to evict its population of more than 1,000 people to make way for the base.

The judgement comes after the UK agreed earlier this year to hand over the islands to Mauritius in a historic move.

Under the deal, which has still to be signed, Diego Garcia would continue to operate as a UK-US military base but Mauritius would take responsibility for any future migrant arrivals. — BBC