Britain has defied an order by the United Nations to return control of an overseas territory to the island nation of Mauritius.

The UN had given the U.K. six months to hand control of the Chagos Islands — an archipelago in the central Indian Ocean — back to Mauritius, but this deadline has now passed.

The government of Mauritius has previously accused Britain of being an "illegal colonial occupier" in the Chagos Archipelago.

The island state claims it was forced to hand over the Chagos Islands to the U.K. in 1965 for independence, which it gained three years later.

"The U.K. has no doubt as to our sovereignty over the British Indian Ocean Territory (BIOT), which has been under continuous British sovereignty since 1814," Britain's Foreign and Commonwealth Office (FCO) said in a statement earlier this month.

"Mauritius has never held sovereignty over the BIOT and the U.K. does not recognise its claim."

Britain's FCO was not immediately available for comment when contacted by CNBC on Friday morning. It has previously insisted it has every right to hold onto the islands.