To make the pickled herring, bring the cider vinegar, allspice berries, peppercorns, bay leaf, sugar, orange zest and juice and onion to the boil until the sugar has dissolved. Place the herring fillets in a heat-proof bowl, pour over the pickling liquid and set aside until cool. Cover and refrigerate for at least 2 days.
To make the cabbage salad, place all the salad ingredients into a large glass bowl and set aside.
To make the vinaigrette, whisk together all the ingredients and toss with some of the cabbage salad, you may not need it all. Cover and set aside for at least 2 hours.
To make the potato salad, place the potatoes into a large saucepan, cover with cold water and bring to the boil. Simmer until softened. Set aside to cool then remove the skins.
Meanwhile, mix the remaining ingredients together then add the potatoes and crush lightly with a fork.
When ready to serve, remove the fish from the pickling liquid and arrange all the components between two serving plates.