How some of the world's biggest banks are helping criminals launder money through the UK capital. The BBC's Andy Verity describes what a major new leak of documents tells us about the flows of dirty money through financial centres. Dr Susan Hawley from the charity Spotlight on Corruption tells us why banks and regulators aren't doing enough to stop it, and Tom Burgis, author of a new book Kleptopia: How Dirty Money is Conquering the World, explains why money laundering is a threat to democracy and freedom.(Photo: London's financial district, Credit: Getty Images)