FCO advice to yachts planning to visit Chagos Archipelago (British Indian Ocean Territory):
The British Indian Ocean Territory (BIOT) is not a tourist destination. Applications from transiting yachts are checked carefully to ensure that a stop there is essential for their safe passage across the Indian Ocean. Where that is not the case, or there is any concern that the visit is not consistent with the policies and laws of the British Indian Ocean Territory (in particular its ambitious environmental objectives) a permit will not be granted.
See https://www.gov.uk/foreign-travel-advice/british-indian-ocean-territory