Use foil to line a roasting tin that is large enough to hold the whole fish, and scatter the base with a thin layer of salt. Rinse the fish but don't dry it, then place it on top of the salt, diagonally if necessary. Tuck the herbs and lemon slices into the cavity and season well with pepper.
Pull the foil up around the fish so that there is a lining of salt about 1.5 cm (¾ inch) thick around the fish.
Scatter the fish with an even covering of salt about 1 cm (½ inch) thick. Drizzle or spray the salt with a little water and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 25 minutes. To check that the fish is cooked, pierce a metal skewer into the thickest area of the fish and leave for a few seconds before removing. If the skewer is very hot, the fish is cooked through.
Lift away the salt crust and peel away the skin. Serve the fish in chunky pieces and then lift away the central bone and head so that you can serve the bottom fillet. Garnish with lemon wedges and herbs and serve with Aïoli (see