Smoked salmon from Loch Fyne holds everything about the sandwich constant and names the one thing that changes: where the fish is from. The build is the unadorned classic, cold-smoked salmon on brown bread with butter, lemon, and pepper. What the name does is point at the source. Loch Fyne is a long sea loch on the Argyll coast, cold, clean, sheltered water, and salmon raised and smoked there is sold under that origin as a marker of quality the way a named oyster bed or a single dairy is. The locality is the lead because in a sandwich this plain the fish has nowhere to hide, and a named provenance is a claim that the fish can stand being looked at this closely.
The craft is the restraint that a good fish demands and a plain build enforces. There is almost nothing here to balance, so every part has to be right: the salmon sliced thin, to translucence, so it folds and layers rather than slabbing; the bread soft and brown so it carries rather than competes; the butter spread to the edges so it seals the crumb against the oil and bridges the salt across to the wheat. Lemon and pepper are the only sharp notes and they go on lightly, because the entire idea is to taste the smoke and the sweetness of the fish itself, and a heavy dressing on salmon worth naming for its source only masks the thing you are paying attention for. This is a sandwich built to get out of the way.
The variations are the rest of the smoked-salmon shelf, each defined by what is set against or under the same cured fish. Cream cheese turns the plain build into a richer, mortared one. Chive or dill works a herb through. The pinwheel rolls the same components into a spiral for the tea tray. Other named Scottish smokehouses make the same quality claim from their own water. Each deserves its own article rather than being crowded in here.