Into a saucepan over a medium heat, combine the potatoes, onions and sausages. Pour in just enough water to cover. Place the lid on the pan and bring to the boil; reduce heat and allow to simmer (adding a little more water if needed) until the potatoes are tender and the sausages are no longer pink in the centre, about 30 to 40 minutes.
Serve with 'juice' from the pan, lots of black pepper and English mustard. Yummy!