To make the cakes, add the mash, crab meat, chopped spring onions, egg, breadcrumbs, sauce, salt and pepper to a large bowl.
Mix all the ingredients to make a paste.
Dust flour on a board, and use your hands to shape 12 patties - the flour will prevent them from sticking.
Refrigerate for 30 minutes to harden up, it will help with the frying.
Heat up the oil in a large frying pan, and fry the cakes in batches, they should need 2 minutes or so on each side until they are golden.
Remove from the pan and transfer to a plate lined with kitchen towel to absorb the excess oil.
Repeat with the remaining patties.
To make the sauce, chop the gherkins and capers finely.
Add them to a bowl together with the mayo and black pepper, and give it a good mix.
Serve the crab cakes with the sauce.