British Nationality could be obtained through your birth, or through the birth of any one of your parents or grandparents, in the British Indian Ocean Territory (Chagos). This arises because of Britain's relationship with Chagos and Britain's Colonial history.
To determine what form of British Nationality you might have, an analysis of your family's history must be done, and then applying it to the Nationality laws governing the British Indian Ocean Territory that have been passed over the years.
STATUS OF CHAGOS
Between 1814 and 31.12.1948, the area came within the Crown’s Dominions. From 01.01.1949 until 07.11.1965, it was part of the UK and Colonies as part of Mauritius. From 08.11.1965 until 31.12.1982, it fell within the UK and Colonies as the British Indian Ocean Territory. From 01.01.1983, it is a British Dependent Territory.
Click here for more information on the status of Citizen of the United Kingdom & Colonies (CUKC), a status achieved by birth in the Colony.