He is the author of fourteen books on Turner, including the bestselling book of all time on the artist. His forthcoming biography of Turner has already been hailed as definitive. Also he has authored books on Hockney, Dalí, Warhol, Brancusi, the Impressionists in London, Pop Art. He lectures at the National Gallery, National Gallery of Scotland, Tate Galleries, and has led many American and European tours.