The Whelk Sandwich is cooked whelks on bread with vinegar; seaside fare, served as a regional specialty in UK (Coastal).
It sits within the Submarine Sandwiches family of French sandwiches — specifically the Coastal Fish & Shellfish cluster, which gathers the regional and stylistic variants that share its frame.
For the broader Coastal Fish & Shellfish tradition that frames this sandwich, see Coastal Fish & Shellfish.