Drain the cans of Princes Tuna Chunks and tip onto a plate. Break the fish into chunks and set aside.
Melt the butter in a frying pan and gently fry the spring onions and garlic for 2-3 minutes. Cool slightly, then mix into the potato with the sweetcorn and parsley.
Add the tuna, season with salt and pepper and mix together. Form into 8 small or 4 large fish cakes and coat them lightly in plain flour.
Beat the egg with 2tbsp cold water. Dip the fish cakes in the egg and coat them in breadcrumbs. Chill until ready to cook.
Heat the vegetable oil in a large frying pan and shallow fry the fish cakes for 4-5 minutes per side, until golden brown. Drain on kitchen paper.