Place the leftover roast chicken carcass, peppercorns, and bay leaf in a large soup pot. Cover the chicken carcass with cold water and simmer gently for 1 hour
After an hour remove the carcass, any whole peppercorns, the bay leaf, and any other bones using a slotted spoon. Leave any chicken pieces in the soup pot. If there's still chicken on the carcass that can be removed and added too.
Using a sieve pour the liquid into a measuring jug to measure how much liquid there is. Add liquid back to soup pot with chicken pieces and make the liquid up to 1.25L total using the chicken stock and extra water if required. Check flavour. You may still need to add an extra stock cube even if no extra liquid is required.
Add the salt, carrots, onion, celery, sweetcorn, and rice. Simmer for 15-20 minutes until the rice and vegetables are cooked.
Season to taste with salt and pepper and serve in bowls with parsley scattered over.