Pre-heat oven to 190ºC/375ºF or gas mark 5 (180ºC for fan assisted ovens). Calculate cooking time allowing 30-40 minutes per kg . Spread all over with butter and season with salt & pepper. Place the bird upside down in a large roasting tin. This will ensure that the juices run in to the breast of the meat, keeping it moist. Loosely cover with silver foil and roast the bird for the calculated time, basting occasionally with the pan juices 45 minutes before the end, turn the cockerel back up the right way, remove the silver foil and continue to cook until the skin becomes crispy. Ensure that the centre of the bird is piping hot and that the juices run clear