Preheat the oven to 220℃/200℃FAN/Gas 7.
Place the lemon zest, parsley stalks, thyme, and celery into the cavity of the turkey. Fill the neck end with some of the stuffing. Put the leftover stuffing into an oven proof dish and set aside.
Shape the stuffed end of the turkey into a neat round and secure the loose skin with fine skewers. Tie the legs with string to give it a neat shape.
Weigh the turkey and calculate the cooking time. Allow 20 minutes per 500g (1lb).
Place 2 large sheets of tin foil on top of the roasting tin so there is plenty of overhang at the sides and place the turkey on top. Spread the butter over the bird, concentrating on the breast area.
Season with plenty of salt and pepper. If using bacon, overlap them across the turkey, concentrating on the breast again.
Fold the sheets of foil loosely over the turkey. Cook the turkey for 30 minutes.
Reduce the temperature to 160℃/140℃FAN/Gas 3 and cook for the remainder of the time.
Thirty minutes before the turkey is ready, fold back the foil and remove the bacon if used to allow the breast to brown, then baste with the cooking juices.
To check to see if the turkey is cooked, pierce the thickest part of the thigh with a fine skewer. The juices should run clear and not pink or red. The internal temperature should reach 165°F (74°C).
Lift the turkey on to a warmed serving platter, cover with fresh foil and leave to stand for 30 minutes before carving.
Meanwhile, put the stuffing in the oven and cook for 25 -30 minutes.