Boil potatoes in salted water to cover. Drain, cool and peel. Mash in large bowl with butter, milk and season to taste with salt and pepper. Set aside. Saute beef until browned, stirring to keep meat crumbly. Season to taste with salt and pepper. Add tomatoes, mushrooms, parsley, tomato paste, worcestershire and gravy. Stir to mix. Add peas and cook about 5 minutes. Turn mixture into casserole. Spread potatoes evenly over meat. Bake at 400 degrees 40 minutes until top is crispy brown.