Preheat the oven to gas mark 5, 375F, 190 °C. Wash the herbs and remove the stalks from the parsley. Chop the parsley leaves coarsely and put them on one side. Chop the parsley stalks, celery leaves and thyme and mix with the bay leaves. Stuff the cavity of the fish with this mixture. Oil a large sheet of kitchen foil and put a line of lemon slices into the cavity and arrange the rest of the lemon long the top of the fish. Season with salt and pepper. Sprinkle generously with the parsley leaves and wrap the fish loosely in the foil, but make sure the edges of the foil are tightly sealed. Put it in the oven and bake for 45 minutes.

To serve, unwrap the foil carefully - there will be a wonderfully herby, lemony, cloud of steam - and remove as much of the liquid that has formed around the fish as possible. You can serve that as a sauce on its own or boil it up briefly with either a knob of butter or a couple of tablespoons of double cream to make it rich and special.

Lay the fish on a serving dish and serve with new potatoes.