My memory, such as it is, tells me it was from a biography of Perkins, written when he was much in the limelight, that I was flipping through in a bookshop shortly after it was published.  I have no memory of the author's name, but it seemed to be a substantial and well-written book.  It may have been the Peter Read book, but I couldn't swear to it.  I'll see if I can track this information down.