Boil the potatoes with skin on. Peel and boil carrots. Peel and dice the eggs. Wash the apple and cut in the same size cubes as the vegetables. In a bowl mix mayonnaise, sour cream, salt, pepper and apple vinegar (it should be a little salty as the vegetables will soak up the taste). Cut gherkins into same size cubes and chop the spring onions. Strain the liquid from the peas and the corn. Squeeze excess liquid out of the cold water shrimp. Mix everything together, add a little oil and let stand for an hour then check seasoning and consistency; if it’s too dry, add some more sour cream and/or mayonnaise.