There is a classic synergy between herrings and mustard, not only because the hot spicy mustard cuts the subtle oiliness of the fish, but because the herring was once landed in large numbers off the East Coast in fairly close proximity to mustard-making country, and many old-fashioned herring recipes will incorporate mustard in some form or another.
Before the 1950s, many fishermen moved to Great Yarmouth to chase the herrings that moved up and down the coast in large numbers to feed during the autumn months, when the sea got colder. Herring traders followed, who would set up shop to sell the preserved herrings - salted, pickled and smoked — to the rest of Europe.