Fifty years after he designed the sleeve for Sgt Pepper’s Lonely Hearts Club Band, Sir Peter Blake is working on a new composite artwork made up of the faces of some of the biggest names in music. Michael Eavis, founder of the Glastonbury festival, asked Blake to create something featuring previous festival acts when he sat for a piece by the artist commissioned by the National Portrait Gallery. “What will you give me in return?” Blake asked Eavis, above. “How about a lifetime’s pass to the festival?” the canny farmer replied. Blake, who attended the first one in 1970, said that this was a poor deal. “At the age of 84, dancing in a muddy field doesn’t hold much appeal any more.” Eavis agreed to…