Prepare your turkey for roasting the day before, Stuff each end of the bird* and rub lavishly all over with at least ¼ lb butter or margarine. Wrap up in well buttered foil and put in a roasting tin. On Christmas Day preheat the oven to Gas Mark 3/325°F/160°C (unless you are doing your roast potatoes in advance). Put the turkey low down in the oven and cook for 2½-3 hours for a 6-8 lb (2.5-3.5 kg) bird, 3-3¾ hours for an 8-14 lb (3.5-6.0 kg) bird and 3¾-4¼ hours for a 14-18 lb (6.0-8.0 kg) bird. Three-quarters of an hour before it is ready, unwrap the foil to expose the turkey so that it will brown, and pour a glass of dry vermouth or white wine over it.
After you have transferred the turkey to a carving board make the gravy. Blend 1 rounded teaspoon (2 x 5 ml spoon) of arrowroot or cornflour with a little water and stir into the pan juices. Let this bubble over the heat until thickened and season to taste. Serve the gravy with the turkey, accompanied by cranberry sauce and bread sauce.