In a large pot over medium high heat, combine the oil, bacon, carrots, onions and celery. Saute for 5 minutes or until bacon is crisp. Stir in the flour until it's dissolved and mixture is pasty.
Slowly add the water, stirring constantly. Then add the bay leaves, salt, lentils, beef stock cubes, thyme, nutmeg, white pepper and potatoes. Stir all together well, bring just to the boil, reduce heat to low and simmer for 3 hours.