In the first of our three part series looking at the money behind shipwrecks, we start with what's been called "the most valuable shipwreck in the world".

The San José is a Spanish galleon sunk by the British off the Colombian coast more than 300 years ago.

The treasure onboard is estimated to be worth $18bn, which means plenty of people are looking for it, and trying to lay claim to it.

A salvage company, the Colombians, the Spanish and a Bolivian indigenous community all say the shipwreck and treasure is theirs.

We hear their claims and find out more about this "holy grail of shipwrecks".

Presented and produced by Gideon Long.

(Image: Wagner's action of Cartagena (depicting the moment the San Jose exploded) by Samuel Scott. Credit: National Maritime Museum, Greenwich, London)