My mother introduced me to these in Coventry. I wonder how she discovered them. Our local chippie was at the bottom of Earlsdon Avenue. I do not remember whether we acquired the butties in the shop itself or whether they were made when we got home. At all events, it proved to be a wonderful and curious mixture of fats and carbohydrates: butter, salt, vinegar, bread and chip.
Many years later, I overheard two of my teachers at prep school talking in surprised disgust at the conduct of a visiting teacher from another school - there for a football match presumably - about how he put his chips between bread and butter. I was longing to contribute to this adult conversation by explaining that this was a chip buttie but was frostily excluded.