Place potatoes in large saucepan, and add enough cold salted water to cover. Bring to a boil, lower heat to medium, and simmer until potatoes are tender, about 20 minutes. Stir in peas and carrots, and cook until carrots are tender, about 1 minute.
Drain vegetables well. When cool enough to handle, cut potatoes in quarters and place in large bowl with peas and carrots.
Meanwhile, cook bacon until crisp, and remove from pan. Crumble and set aside. Add vinegar, mustard, and pepper to drippings in pan, and whisk to mix. Pour warm dressing over potato mixture. Sprinkle with bacon, and stir to coat.