BBC – Diego Garcia, a remote island in the Indian Ocean, is a paradise of lush vegetation and white-sand beaches, surrounded by crystal blue waters.

But this is no tourist destination. It is strictly out of bounds to most civilians – the site of a highly secretive UK-US military base shrouded for decades in rumour and mystery.

The island, which is administered from London, is at the centre of a long-running territorial dispute between the UK and Mauritius, and negotiations have ramped up in recent weeks.

The BBC gained unprecedented access to the island earlier this month.