Trussing a bird before roasting it is not essential but it undoubtedly gives the bird a neater shape, which looks better when it is served at the table.
First remove the wishbone. Lay the bird on its back on a board. Pull back the flap of skin at the neck end and find the tip of the wishbone with a sharp small knife. Run the knife along the inside of the bone on both sides, then on the outside. Cut deeply enough to free the bone and make it clearly visible. Take care not to cut into the breast meat. Run the knife just behind the wishbone, then use your fingers to lift and twist it free.
Cut a piece of kitchen string about 4-5 times the length of the bird, then loop it around the narrowest part of each leg, pulling the ends tightly to bind the legs together.
Bring both ends of the string along either side of the breast, nestling it between the breast and the legs.
Take the string around the outside of the wings, flip the bird onto its breast and draw up the nub at the neck. Cross the ends of the string over the nub.
Holding the ends of the string and the nub, flip the bird onto its back again. Tie the ends of the string together into a tight knot at the nub of the neck.
Here you have the trussed bird, ready for the oven.