In a large plastic bag, combine 1/2 teaspoon of the salt, 1/2 teaspoon of the pepper and 1/4 cup of the flour. Put lamb pieces into bag (6-8 at a time), and shake bag until lamb is completely coated.
In a large pot or Dutch oven, melt butter over medium heat. When pot is hot, brown lamb pieces (about 10 at a time) on all sides. Remove browned lamb to a plate; set aside.
When all the lamb is browned, return it to pot. Add 2 cups of the water plus tomato sauce, parsley, thyme and the remaining 1 teaspoon of salt and 1/2 teaspoon of pepper. Bring to a boil, reduce heat and slowly simmer, keeping pot tightly covered, until lamb is tender (about 45 minutes).
Add carrots, and simmer for 20 more minutes. Add onions, diced turnip and potatoes. Simmer, covered, for another 45 minutes, or until vegetables are tender.
In a small bowl, add the remaining 1/4 cup of flour and 1/4 cup of cold water; blend until smooth. Stir into stew to thicken gravy. Add peas and bring stew to a boil. Simmer for another 20 minutes.