Rinse the lentils in cold water and pick out any stones, then set aside.
Fry the bacon bits in a large pan for 3-4 minutes until the fat runs and they start to crisp at the edges.
Add the onion and carrots and cook for 5 minutes until the onion is soft.
Tip in the lentils, potato, thyme and stock. Bring to the boil, then reduce the heat and simmer for 25 minutes until the lentils have broken down and the potato is tender.
Season well with salt and pepper. Blend with a stick blender if you prefer a smooth soup, or leave it chunky.
Add a splash of milk at the end if you like a creamier texture, and serve with bread.