Dredge a fish fillet through the flour and knock off the excess, then dip it in the beaten egg. Hold it up to drain off any excess egg, and place it in the breadcrumbs. Turn the fish over until the fillet is evenly coated with a good layer of crumbs and set it to one side. Repeat with the other fillets. You can put the breaded fillets into the fridge to firm up the breadcrumbs if you wish.
You will need to preheat the oil in a large pan to 180oC to fry the fish. If you do not have a frying thermometer, take a large breadcrumb and drop it in the fat; when it sizzles, starts to colour and rises to the surface the oil is ready. Fry the fish in the oil for 3 minutes or until light and golden, depending on the thickness of the fillets. Drain them on pieces of kitchen paper to remove any excess fat.
Sprinkle the fish with Maldon salt, and serve immediately with lemon wedges and tartare sauce.