Put the garlic cloves and half the herb sprigs in the body cavity of the chicken. Pat the chicken dry with kitchen paper and rub the oil all over the outside of the bird. Strip the leaves off the remaining herb sprigs and rub over the bird, with a little salt and pepper.
Place the chicken, breast-side up, in a roasting tin. Roast in a preheated oven, 220°C (425°F), Gas Mark 7, for 10 minutes. Turn the chicken over, breast-side down, reduce the oven temperature to 180°C (350°F), Gas Mark 4, and cook for a further 20 minutes. Finally, turn the chicken back to its original position and roast for another 25 minutes until the skin is crisp and golden. Check that the chicken is cooked by piercing the thigh with a knife. The juices should run clear, with no sign of pink. If not, cook for a further 10 minutes.
Transfer to a warmed serving plate and leave to rest for 5 minutes before serving with the pan juices.