In Scotland the bread is the morning roll, and the bacon roll is named for it rather than for anything done to the bacon. The Scottish morning roll is dense and heavily floured, softer in the bite than an English bap but with more weight to the crumb, dusted thickly enough on top that the flour comes off on your fingers. It is a substantial roll that still gives easily, closer to bread than to anything crusty, and the heavy dusting is part of its character rather than incidental. The roll is the variable that makes this Scotland's version; the bacon inside is the part that holds steady wherever the sandwich is made.
The dense, floury crumb is what the morning roll brings once hot bacon goes in. Rashers fried until the fat has rendered and the edges crisped carry grease and salt that has to be taken up without leaking, and the close crumb soaks a measured amount into its base, going heavy and rich there while the floured top stays dry and faintly chalky against the lip. The build is plain and the timing is the discipline: butter the roll while it is cool so the fat does not pass straight through the dense crumb, lay the bacon in straight off the pan so the heat keeps working, keep any sauce inside so it does not run down the floured outside, then close it and eat before the steam has fully softened it. The contrast across one roll is the point: a dry chalky top, a base gone dense with bacon fat, the rashers salt and chew between.
Travel south or to a different corner and the same sandwich answers to other words. It is a bap across much of England, a barm in Lancashire, a cob through the East Midlands, a batch around Liverpool and Coventry, a stottie around Newcastle, and in Aberdeen it moves onto the laminated butterie entirely. Set the bread word aside and it is a bacon butty, or a bacon sarnie in passing. The fillings stretch the way the names do: a fried egg with a yolk to be managed, a sausage with or instead of the bacon, and across Scotland a slice of square sausage or a tattie scone folded in alongside. Those deserve their own articles rather than being crowded in here.