Britain has apologised for the "shameful" way it evicted islanders from the Chagos archipelago in the Indian Ocean, but insisted Mauritius was wrong to bring a dispute over sovereignty of the strategic atoll group to the United Nations' top court.

The apology came on the first day of a hearing on the future of the islands, the site of a key UK and US military base, at the International Court of Justice in the Hague.

Mauritius has asked the ICJ for a legal opinion on sovereignty over the archipelago on the grounds they were “unlawfully” separated and incorporated it into British Indian Ocean Territory ahead of independence.

The hearing is seen as a critical test of Britain’s diplomatic clout in the Brexit era, after it failed to rally enough to support to prevent the UN General Assembly adopting the resolution that led to this week's hearing.

Britain paid Mauritius £3 million for the Chagos Islands, which it then reassigned to British Indian Ocean Territory, in 1965. In the 1970s Britain forcefully evicted around 2,000 local residents to make way for a sprawling US military airbase on the largest island, Diego Garcia.

They and their descendants have been campaigning for the right to return home ever since.