Short, sweet interview clip (in which Dalek operator Nick Evans also appears briefly) from the feature Future Memories (2003) on the DVD of The Dalek Invasion of Earth.
If you like this, I recommend watching the whole thing - at 45 minutes it's a bit of a commitment, but it's all interview footage from various people, and there are some good anecdotes (including more from Davies, who's a pleasure to listen to).