The UK has been condemned for ignoring a United Nations deadline to hand the Chagos Islands back to Mauritius.

A six-month deadline to return control of the overseas territory came and looked set to pass on Friday, with the UK refusing to recognise Mauritius's claim of sovereignty over the islands. The UN overwhelmingly voted in May to set the six-month deadline for UK withdrawal from the Indian Ocean archipelago in a major diplomatic blow.

The islands have been at the centre of a decades-long dispute over Britain's decision to separate them from Mauritius in 1965 and set up a joint military base with the US on Diego Garcia, the largest of the isles.

Olivier Bancoult, from The Chagos Refugee Group, led a peaceful protest of few dozen islanders outside the British High Commission on Mauritius on Friday, where many of the displaced Chagossians live after being barred from their homelands.

"This peaceful demonstration is intended to show the discontent of the Chagossians and Mauritians at Britain's refusal to respect the United Nations resolution... giving her six months to end the illegal occupation of Chagos," Bancoult said.

Protestors waved flags and held up placards.

The UK evicted Chagossians from the archipelago between 1967 and 1973 so the US could erect a military base on Diego Garcia, the largest island in the group.