Strip the leaves from 1 sprig thyme and chop; combine with the flour, allspice, 1/2 teaspoon salt and 1/4 teaspoon white pepper in a large bowl. Add the beef and toss to coat. Put the potatoes, carrots, the remaining 2 thyme sprigs, the ginger and garlic in a 5-to-6-quart slow cooker. Add the beef, reserving any excess seasoned flour in the bowl. Whisk 1/2 cup water and the Worcestershire sauce into the reserved seasoned flour, then add to the slow cooker. Pour the tomatoes on top. Cover and cook on low 7 hours or on high 4 hours. Add the scallions to the stew and season with salt. Divide among bowls and serve with hot sauce.