Put the chicken in a saucepan in which it fits quite snugly. Add the carrots, celery, onion, thyme, parsley sprigs, bay leaves and peppercorns. Cover with water and bring to a gentle simmer. Cover and cook very gently for 1 1/4 hours until the chicken is cooked through. Lift the chicken from the liquid and leave to cool. Strain the liquid and reserve.