Preheat the oven to 180 C / Gas 4. Lightly grease a 3-pint casserole dish.
Arrange half the potatoes in the base of the casserole; cover with half the onions and all of the carrots. Top with remaining potatoes and onions; season with salt and pepper.
Pour over the baked beans; arrange the sausages on top. Pour over the soup; cover the dish.
Bake in the centre of the preheated oven until the vegetables are tender and the sausages are well browned, about 2 1/2 hours.