Sarah Montague speaks to Duff McKagan, a rock musician who nearly drank himself to death. He is one of the founding members of Guns N' Roses, the rock band who became as well known for their bad behaviour as for their music. For McKagan that stopped when, as he puts it, his pancreas exploded. It prompted him to sober up, go to university and now, alongside his finance column for Playboy, he has his own wealth management firm. How does a bad boy of rock become a businessman?