There's a great post on Richard Williams' blog about his role in Abba's rise to world domination. It even has a walk-on part for The Human League, in the Melody Maker offices:
“Sorry, Ian,” I said, “but I really have to listen to this — it’s the new Abba single.” A look of horror crossed his face. The two people with him swung round in amazement. They were Phil Oakey and Joanne Catherall from the Human League, then at the very beginning of their journey to pop stardom.