For many, Sgt Pepper's Lonely Hearts Club Band is The Beatles at their best. When it came out on 1 June 1967 it was unlike anything that had come before it. Experimental and immersive, it pushed musical boundaries. Half a century on, it remains one of the most influential albums of all time, as Beatles author Steve Turner explains: "It was artistically aspirational at a time when most of their contemporaries were still playing beat music of some kind or another. "They had these great ambitions. Paul was starting to go to the theatre, George was listening to Indian music,...