Michael Buerk and Bettany Hughes continue the countdown of the 50 greatest treasures found by the British public. Bettany goes diving for Roman treasure, Michael Portillo investigates a two-headed 2000-year-old coin revealing a political coalition, John McCarthy tells the story of a jewel-encrusted cross, a jar full of gold coins found on a Hackney council estate reveals a story about the Nazis, and John Sergeant checks out a hoard of French coins which could be forgeries.