While the turkey is roasting, place the giblets, turkey neck and clipped turkey wing tips into a large saucepan with the carrots, celery, water and chicken stock. Bring to the boil over medium heat, skim off any foam that forms on the top, reduce heat to low and simmer the stock for 3 hours. Strain the stock, skim off the fat and set aside. There should be about 1 litre of stock.
Skim off and discard all but 4 tablespoons of the fat from the drippings in the roasting tin and place the roasting tin over medium heat. Whisk in the flour, then cook and stir the flour mixture until it becomes pale golden brown, about 5 minutes. Whisk in the stock and tomato puree; bring to the boil, simmer for 5 minutes, then whisk in the redcurrant jelly. Simmer for 10 more minutes. Season to taste with salt and black pepper.
This recipe assumes that the turkey will produce about 350ml of drippings after skimming. Actual amount may vary.