Heat the oil in a frying pan. Gently fry the sausages for about 5 minutes, turning frequently until golden but not cooked through. Remove from the pan and set aside. Tip away all but 2 tsp of fat from the pan.
Add the bacon and fry for 2 minutes. Add the onion and fry for 8 minutes, stirring frequently until golden. Add the garlic and fry for 1 minute, then turn off the heat.
Arrange half the potato slices in the base of the cooking pot. Spoon the bacon and onion mixture on top. Season well with salt and pepper, and sprinkle with the sage. Cover with the remaining potato slices.
Pour the stock over the potatoes and top with the sausages. Cover with the lid and cook on high for 3-4 hours; or til the potatoes are tender and the sausages are cooked through.