Robert Louis Stevenson ' s famous " Treasure Island " comes to the city of London , when a stage version of the famous story opens at the Mermaid Theatre , Puddle Duck , Blackfriars . Pictured during a rehearsal are three of the main characters , left to right : Spike Milligan as " Ben Gunn " , William Rushton as " Squire Trelawney " and Barry Humphries as " Long John Silver " . 13 December 1967