From the mid-1970s the humble 7-inch vinyl single was joined by a much grander relative - the 12-inch single. It reached its peak in 1983 with "Blue Monday", by New Order, probably the biggest-selling 12-inch single of all time. Music Journalist and co-founder of ZTT Records Paul Morley talks to Peter Hook of New Order about how "Blue Monday" was written, and to designer Peter Saville about the famous sleeve.