The Wotsits sandwich is the crisp sandwich taken to its most particular extreme: a specific cheese-flavoured corn puff trapped against soft buttered bread. A Wotsit is not a potato crisp but an extruded, baked maize puff coated in a powdery cheese seasoning, so it brings two things a normal crisp does not. It crunches and then dissolves, the puff collapsing and melting on the tongue rather than staying hard, and it carries an intense artificial-cheese coating that ends up smeared across the bread. The defining fact of this sandwich is that texture: a brittle shatter that turns to nothing in the mouth, pinned between two yielding faces.
The craft, such as it is, lives in the butter and the press. Butter is structural, gripping a very light, escape-prone filling so the puffs do not spill out of the open edge, and adding the fat a dry maize puff and dry bread both lack. The press is the technique: pushing down crushes the puffs in place so a loose, airy heap becomes a single thin layer that holds for a few bites, which is the only way the crunch survives being assembled. The bread is chosen soft and plain so it compresses to the puffs rather than fighting them, and the sandwich is made and eaten close together, because a Wotsit goes stale against buttered bread fast and the orange dust quickly works the bread soft.
The variations are entirely in the snack aisle, and they are a national in-joke with real internal logic. Monster Munch brings a denser, chewier corn shell; a standard cheese-and-onion or salt-and-vinegar crisp swaps the melt-away puff for a hard potato shard; the plain crisp sandwich is the bare generic statement of the same trapped-crunch idea. Each deserves its own article rather than being crowded in here.