[Police] Message in a bottle

I received an email from a japanesse TV producer who is making a program called "Song to Soul" which is an hour long music documentary to explore legendary songs. They are working now on Message in a bottle. He asked me if I knew the history behind the writting of the song as when and where it was writting. He told me they´ve been told it could have been writting in tha back of a bus probably while touring USA for the first time. From Lyrics and some interviews I checked I could not find any mention of this. Does anybody know something about this story? Thanks, Joe