Stir the flour and salt together in a bowl, then form a well in the centre. Gradually pour in the water, whisking in the flour to make a smooth batter. Leave for 30 minutes.

Cut the potatoes into strips about 1cm/1/2 in wide and 5cm/2 in long, using a sharp knife. Place the potatoes in a colander, rinse in cold water, then drain and dry them well.

Heat the oil in a deep-fat fryer or large heavy-based saucepan to 150C/300F. Using the wire basket, lower the potatoes in batches into the oil and cook for 5-6 minutes, shaking the basket occasionally until the potatoes are soft but not browned. Remove the chips from the oil and drain them thoroughly on kitchen paper.

Heat the oil in the fryer to 190C/375F. Season the fish. Stir the batter, then dip the pieces of fish in turn into it, allowing the excess to drain off.

Working in two batches if necessary, lower the fish into the oil and fry for 6-8 minutes, until crisp and brown. Drain the fish on kitchen paper and keep warm.

Add the chips in batches to the oil and cook them for about 2-3 minutes, until brown and crisp. Keep hot until ready to serve, then sprinkle with salt and serve with the fish, accompanied by lemon wedges.