Preheat the oven to 200°C (400°F/Gas 6). Sit a wire rack in a baking tin so the pork won’t touch the bot tom of the tin and will crisp on all sides. Put the pork on a board, skin side up, and prick the rind here and there with a metal skewer or sharp pointed knife — it’s quite tough but you will manage. Turn the pork over and rub the olive oil into the underside — this will also help the herbed salt stick. Scatter 2 tablespoons of the herbed salt over evenly. Roll up compactly and tie it with string in 3 or 4 places so it holds its shape. With some oil still on your hands, rub the skin all over, then rub the remaining herbed salt on.
Sit the pork on the rack in the tin and dribble a little water into the tin. Roast in the oven for about 1 hour 45 minutes, lowering the temperature to 180°C (350°F/Gas 4) for the last 30 minutes. Dribble in a little extra water if the bottom of the tin is threatening to dry out at any point. The outside of the pork will be deep golden and crispy, and the inside soft (roast for an extra 10 minutes or so, if necessary). Serve hot in slices, with bread.