Heat the grill to a medium-high heat.
Peel and chop the potatoes into chunks, and place in a pan of water. Bring to the boil, cover and cook for 12-15 mins until tender. Drain and leave to cool slightly,, then mash.
Meanwhile, season the salmon fillets and grill for 5-6 mins until just cooked. Cool for a few minutes, then break into large flakes.
Mix the potato, 2 tsp tomato ketchup, 1 tsp English mustard, the lemon zest and season with salt and pepper to taste. Lightly mix in the salmon, taking care not to break it up too much.
Shape into 4 large fish cakes.
Put 3 tbsp plain flour, 1 beaten egg and 100g dried breadcrumbs in 3 shallow dishes. Dip the cakes into the flour, dust off any excess. Then, dip in the egg, and finally coat in breadcrumbs
Heat 4 tbsp sunflower oil in a large pan. Fry the cakes over a medium-low heat for 3-4 mins each side until deep golden and heated through.
Serve with salad and lemon wedges