Ah, pickled fish. One of the few real danger zones when it comes to matching grub and grog. Most of the time, let's face it, you can happily eat almost anything with anything and not get into too much strife: there are hardly any combinations of food and wine that are disastrous enough to make you gag or screw up your face in disgust. But pickled fish, especially pickled oily fish, is one of them. Try this mackerel with, say, a nice, eager-to-please chardonnay, and the vinegar in the pickle - aided and abetted by the fishy oils - will make the wine taste like battery acid. No, what you need with this thoroughly northern European-inspired dish is a pint of that thoroughly northern European liquid staple, beer. And I'd be inclined to veer towards a traditional English style of beer - what the Poms call "bitter" (for rather obvious reasons). The moderate, even mild levels of alcohol in a good bitter give it a rounded, potato-friendly, pleasing body, but the bitterness on the finish is just what you need to cut through the creaminess of the mayo and the oiliness of the fish. And the vinegar won't clash with the beer in the same way it will with wine - indeed, sometimes I think vinegar and beer were meant to be together (I'm thinking pickled onions, salt and vinegar crisps, fish and chips on the beach…).
Deliciously sharp pickled mackerel and creamy potato salad are destined to be paired with an English-style bitter.