London's Tate Modern is the world's most popular museum of modern and contemporary art, with 5m visitors a year. Only 20 years ago it was the shell of a defunct power station on the banks of the Thames. Now it is expanding with a £260m extension that opens next month. Edwin Heathcote, the FT's architecture critic, previews the new building with one of the architects, Jacques Herzog, and Tate director Nicholas Serota. For information regarding your data privacy, visit acast.com/privacy