The chip butty is the chip sandwich with the bread question dropped entirely, and that is its whole identity. Where a chip bap or a chip barm announces a particular regional roll, the butty assumes the plainest carrier of all: soft sliced white bread, buttered, folded over hot chips, pressed down. There is no roll to argue about, no protein, no pretence. The name itself, butty, just means buttered bread, and the sandwich is exactly that promise kept. It is the form stripped to its argument, which is that a starch can be a filling if the fat and the bread are handled right.
The craft is timing, the butter, and the press. The chips have to be hot enough to melt the butter on contact, because that emulsion of fat and potato is the only sauce the sandwich has and a cold chip will not make it. The bread is soft and plain so it yields to the chips rather than competing with them, and it is buttered right to the edges so the slick forms inside the fold instead of soaking the slice into paste before it reaches the mouth. Thick-cut chip-shop chips suit it, crisp at the edge and floury in the middle, laid in a flat layer so the bread folds evenly over them. The press is the step that makes it a sandwich rather than chips in a napkin: pressing the folded bread down binds the loose chips into something that holds together for a few bites. Salt and plenty of malt vinegar goes on the chips before folding, the vinegar soaking into the soft bread as part of the point rather than a problem to keep out.
The variations are the same idea under other words and with the addition turned up. It is a chip bap, a chip barm, or a chip cob once a particular regional roll is named instead of plain sliced bread. Pour chip-shop curry sauce, gravy, or mushy peas over the chips and the butty crosses from snack to meal. Those deserve their own articles rather than being crowded in here.