Jeremy Paxman: And these scraps of paper which you've filed elegantly in a carrier bag, they're plot ideas or...

JK Rowling: Well some of them are totally redundant now because its been written and I keep them out of sentimentality's sake, I suppose. But some of it has backstory in it like this - in here is the history of the Death Eaters and I don't know that I'll ever actually need it - but at some point - which were once called something different - they were called the Knights of Walpurgis. I don't know if I'll need it. But I like knowing it. I like to keep that sort of stuff on hand.