Britain suffered an overwhelming defeat at the UN on Wednesday over its control of the Chagos Islands, home to the Diego Garcia military base that is leased to the US.
The vote among members of the UN General Assembly came in a non-binding resolution but called on Britain to withdraw its colonial administration and cede the territory to Mauritius within six months.
Only six countries including Britain and the US opposed the vote in the 193-member assembly, while 116 voted in favour and 56 abstained.
African countries proposed the resolution over the Chagos Islands, known as the British Indian Ocean Territory, which is considered to be one of the last remaining vestiges of empire.
The Diego Garcia military base has been a departure point for long-distance bomber raids and rendition flights carrying terrorism suspects.
Mauritius claims sovereignty over the islands. An advisory opinion of the International Court of Justice in February said that Britain should hand over control.
Mauritius passed its goal of 100 votes in favour but Britain's permanent representative to the UN, Karen Pierce, later said that the large number of abstentions indicated that many countries agreed the dispute should be resolved bilaterally, rather than at the UN.
Britain took possession of the Chagos Islands in 1814 and kept them after Mauritian independence in 1968.
Three years earlier Britain had secretly leased Diego Garcia, one of the islands, to the US for 50 years to use it as a military base. In 2016 the deal was extended to 2036.
The people of the islands were forcibly evicted and have long been fighting Britain in legal cases to return.
The International Court of Justice , the UN's highest, heard testimony from former islanders that they were “uprooted like animals” and loaded on to a ship.
The evictions were described in a British diplomatic message at the time as the removal of a “few Tarzans and Man Fridays".
The court's judges said the agreement between Britain and Mauritius had not been “based on the free and genuine expression of the will of the people concerned”, and that the break-up of the colony was against international law.