The leaked “Panama Papers” show how a Panamanian law firm, Mossack Fonseca, secretly shepherded a web of offshore accounts that resulted in billions of dollars in transactions passing through its doors. Its client list includes some of the world’s wealthiest people, from members of Russian president Vladimir Putin’s inner circle to the prime minister of Iceland. Tom Burgis talks to Vanessa Houlder, FT tax correspondent and Alex Cobham, head of research at the Tax Justice Network, about the significance of the revelations.