Put the cubed bacon into a large saucepan, place over a moderate heat, and cook until the fat runs. Add the leeks, celery, and garlic, and cook for a few more minutes before adding the tomatoes, parsley, and mixed herbs. Stir the vegetables, and season with salt and pepper. (It may be necessary to add a little oil if there is not sufficient bacon fat.) Cook for 5-10 minutes.
Stir in the