Coat the potato wedges in 4 tablespoons of the oil and toss with the salt flakes. Transfer to a baking sheet and roast in a preheated oven, 200°C (400°F), Gas Mark 6, for 20–25 minutes until golden in places.
Meanwhile, cut each chicken breast in half across its width to make 2 thin chicken breasts. Put the flour in a large bowl with the mustard powder, pepper and parsley and season with a little salt. Mix well, add the chicken pieces and toss well to coat lightly in the seasoned flour.
Heat the remaining oil in a large frying pan and cook the chicken, turning once, over a moderately high heat for 8–10 minutes until golden and cooked through. Serve the chicken with the roasted jacket wedges and with mayonnaise flavoured with mustard and a rocket salad, if liked.