Carl Allen is a multi-millionaire former businessman who ran a trash bag company in the US.

He's now the owner of an island in the Bahamas, a philanthropist and deep-sea treasure hunter, scouring the seabed for sunken Spanish galleons, slave ships and long-lost treasure. He tells us about his relentless search for one Spanish galleon that’s fired his imagination for the past 40 years. We discuss the ethics of treasure hunting and his belief that the best way to bring up relics from the bottom of the ocean is through PPPs - public-private partnerships. Produced and presented by Gideon Long

(Image: Carl Allen on a boat with some treasure. Image credit: Brendan Chavez at Allen Exploration)