Five children stranded on the remote island of Diego Garcia in the Indian Ocean since October 2021 have won a case to be protected from harm in the same way as British children.

The supreme court of the British Indian Ocean Territory (BIOT), sitting remotely in London, has ruled in favour of some of the Tamil asylum seekers on the island including the five children and found that the key protections in the UK’s Children Act applies to the children on the island.

Judge Margaret Obi, acting judge of Diego Garcia’s supreme court, rejected the arguments of lawyers for Paul Candler, the island’s commissioner, who said that the Children Act did not apply on Diego Garcia and that he was not bound by its obligations. The case included applications for wardship for the children following concerns about their wellbeing and safety on the island.

In a previous case the court heard evidence from the UNHCR that the conditions the 61 asylum seekers on the island including 16 children are living in amount to arbitrary detention. The refugee agency called for the group to be urgently relocated from the island.

The asylum seekers, mainly Tamils from Sri Lanka, arrived on the island in October 2021. They were rescued and taken to Diego Garcia after a boat they were travelling in, hoping to reach Canada to claim asylum, got into difficulty.

The UNHCR found that the asylum seekers fall under the effective control of the UK government.

The UN inspectors heard allegations of sexual harassment and abuse against women and children by other asylum seekers, and identified high levels of mental distress and significant risk of suicide and attempted suicide.

They found the detention of 16 children among the 61 “particularly troubling” and said at least some of those found to be in need of international protection should be transferred to the UK.

The UNHCR also said the asylum seekers are held in a fenced-in area the size of a football pitch, guarded by G4S staff. They are not allowed to cook for themselves and have been bitten by rats, which are “ubiquitous” on the island and have gnawed holes in their tents. Their movements are severely restricted and are only recently permitted to leave the camp to go a small beach area alongside to the camp at designated times, under close supervision.

In Tuesday’s ruling the court found that the commissioner has a duty to properly safeguard, investigate harm and promote the welfare of the children on Diego Garcia under the Children Act 1989.

In her ruling judge Obi said: “In the absence of a specific local law the law of England applies.”

She added: “There cannot be any concept of lesser justice in the BIOT. The same principle applies with regard to safeguarding and promoting the welfare of children.”

Lawyers for the asylum seekers from Leigh Day and Duncan Lewis welcomed the ruling.

A further hearing relating to the asylum seekers’ claim that they are being unlawfully detained on Diego Garcia will take place on 15 April.