In times like these, what is art worth? And what is art for? The big moment for publicly funded art in Britain was the Second World War. "Something absolutely remarkable happened during the war", says actor Simon Callow. "The theatre suddenly was right at the heart of society." After the war, the idea of "art for all" led to the founding of the Arts Council - "very much a response to the distress, the fear, the uncertainty of war." Alan Yentob asks if culture can play that role again today.