I believe BEng distinguishes "fillet" (with a final t) from "filet" (without), the former having been borrowed from French when it still had a /t/ at the end, a

I believe BEng distinguishes "fillet" (with a final t) from "filet" (without), the former having been borrowed from French when it still had a /t/ at the end, and the latter being a later re-borrowing (usually in phrases like filet mignon). Something like "filet of fish sandwich" comes across as a humourously fancy name for a pretty ordinary meal.