Put the oil in a frying pan over a low heat , add the onions then sprinkle over the salt.
Cook uncovered for about 30 to 40 minutes, stirring occasionally.
Increase the heat to medium and stir in the sugar for 5 minutes until the onions are really soft.
While the onions are cooking, prepare the Cumberland ring sausage. To keep their shape while cooking I've used 2 cocktail sticks pushed through the rings.
Mix the honey and mustard together in a small dish.
Place the cumberland ring sausage on a grill (broiler) pan.
Preheat the grill to medium and grill for 8 minutes.
Turn the sausages over and use the pastry brush to cover the sausages with the honey and mustard mix.
Cook for 10 minutes.
Turn the sausages again and cover this side with the honey and mustard mix.