Coat the lamb: Dust the lamb shanks with flour and season with salt and pepper in a large bowl.

Brown the shanks: Heat a skillet and sear the coated lamb shanks until browned on all sides, about 5-7 minutes.

Combine ingredients: Layer browned lamb shanks with diced carrots, chopped celery, diced potatoes, and diced onion in the slow cooker. Add crushed tomatoes, crushed garlic, tomato paste, Worcestershire sauce, red wine, water, and crushed beef stock cubes, followed by fresh thyme and bay leaves. Season with salt and pepper.

Cook slowly: Cover and set the slow cooker to low, cooking for 8 hours until lamb is fork-tender and vegetables are soft.

Serve warm: Dish out and enjoy with the rich sauce and veggies. Garnish with fresh thyme if desired.