Preheat oven to 180°C, 350°F, Gas Mark 4. If using a frozen turkey, ensure it is thoroughly thawed and no ice crystals remain in the body cavity. Remove giblets if necessary. (Use giblets to make stock for gravy). Wipe the turkey inside and out with either a clean damp cloth or kitchen paper. Pat dry.
Weigh the turkey and calculate the cooking time allowing 20 minutes to the kg plus 90 minutes.
Place in a roasting tin. Cover loosely with foil and cook in the preheated oven for calculated cooking time. Remove foil for the last 40 minutes of the cooking time.
Continue to cook for the remaining time, basting occasionally with the turkey juices, until cooked and the juices run clear when the thigh is pierced with a skewer. (Try to avoid opening the oven door too often during cooking). Add a little of the pan juices to the gravy.
Transfer to a platter, cover loosely with foil or a clean tea towel and leave to rest for at least 20 minutes before carving. Serve with roasted potatoes and parsnips, sprouts and carrots.