Start by peeling the potatoes and cutting into bite-sized pieces. Boil in salted water until the potatoes are soft enough to fall apart when prodded with a fork.
While the potatoes cook, remove the crusts from the white bread and pulse in a blender to make breadcrumbs. Then, spread them out on a baking tray and toast under the grill until golden and crispy. Crush with a rolling pin to make them really fine.
Once the potatoes are cooked, mash them with a little milk until soft and fluffy, and leave to cool and firm up for about ten minutes.
Stir the smoked salmon trimmings, Sweet Pickled Cucumber and chopped fresh parsley through the mashed potato, with a squeeze of lemon. Season with salt and black pepper.
Spread out the flour on a plate, and beat the egg in a bowl with a fork. Shape the mashed potato mixture into patties, then dip each one first in flour, then in beaten egg, and then in breadcrumbs.
Pour the vegetable oil into a small saucepan to a depth of about 1cm, and heat until a crumb dropped into the oil sizzles and fizzes on the surface. Then fry the fishcakes until golden on both sides, and serve with wedges of lemon.