Put the lentils, carrots, swedes, celery and onions into the large pot of boiling water. If desired, add in the tatties.
Place ham stock cubes into a heat-resistant jug. Add 3 pints of boiling water and mix the stock cubes with a spoon until entirely dissolved. [If ham stock is not available locally as cubes, boil down a ham bone and use the stock remaining.]
Add the sprig of fresh parsley and the fresh bay leaves.
Simmer for an hour or until vegetables are tender. Stir regularly and add more water if necessary to stop the soup becoming too thick.
Serve with hot, crusty bread.