1. Preheat oven t 180° / 350° / Gas Mark 4, 10 minutes before roasting. Weight the turkey and calculate cooking time, allowing 18 minutes to 450g / 1lb.
2. Wipe the turkey with a clean damp cloth and sprinkle the cavity with salt an pepper. Halve the lemons and place inside the body cavity with a few whole basil sprigs.
3. Place breast side down in the roasting tin then place in the oven and roast in the oven for the calculated cooking time. (By cooking the turkey upside down, the natural juices will baste the turkey as it cooks.) Twenty minutes before the end of cooking time, turn the turkey over and continue to cook for the rest of the cooking time. Check the turkey is thoroughly cooked by inserting a long skewer in the thickest part of the thigh. If after 1 minute the juices run clear the turkey is cooked.
4. Remove from the oven, place the turkey on a serving plate, cover with a large sheet of tinfoil and allow to stand for 20 minutes. Garnish with lemon wedges and extra basil, serve.