The Rainbow Sandwich by Marjorie Darke

This little book is now out of print. It is an easy read suitable for 9-12 year olds. The little ghost called Grey is just having a snooze in the cellar, when suddenly there's a terrible noise and the place falls in around him. He finds that his old haunting place has disappeared, but when he meets Mark, someone who can actually see him, his bones begin to feel at home again and they search for his old haunting-ground. It is hard to find information about the author.