Bring the stock to a boil over high heat in a medium pot, then reduce the heat to medium-low and add the chicken neck and giblets and any other trimmings. Simmer for 30 minutes, until the stock reduces by about one-third. Strain the stock, discarding solids.

Meanwhile, melt the butter in a medium saucepan over low heat. Add the onion and cook for 6 to 8 minutes or until just soft, then stir in the bread crumbs, parsley, thyme or savory, and chives, and season to taste with salt and pepper. Cook for about 3 minutes, then remove from the heat and set aside to cool to room temperature.

Preheat oven to 400°F/200°C (Gas Mark 6).

Season the chicken all over, inside and out, with salt and pepper, then fill the cavity with stuffing, being careful not to pack it too tightly. Push thyme sprigs lightly into the stuffing so that they protrude. Secure the opening with a small skewer, then roast the chicken on a rack in a roasting pan for 20 minutes. (Put the leftover Stuffing in a small baking dish and put it in the oven with the chicken, if you like.) Reduce the heat to 350°F/175°C (Gas Mark 4) and continue roasting for about 20 minutes per 1b/40 minutes per kg (not counting the first 20 minutes). To test for doneness, stick a skewer into the thigh; if the juices run clear, the chicken is done.

When the chicken is cooked, remove the rack with the bird still on it and set aside to rest. Spoon the excess fat out of the roasting pan, then put the pan on the stove top over low heat. Sprinkle in the flour and stir until a roux forms. Add the reserved stock. Increase the heat to high and deglaze, scraping up the browned bits from the bottom of the pan. Continue to cook, stirring constantly, until the gravy is thick.

Carve the chicken and serve with the gravy on the side.