Many of Diana Wynne Jones' novels are set in our world, World 12B, or at least a world that closely resembles it. The Chrestomanci novels, mostly take place in Series 12, with the exception of Conrad's Fate. There is really nothing to say about Our World, as we live in it and we should know.
Although the concept isn't mentioned, the wizard Howl (originally Howell Jenkins of Wales ) is actually from this world.