Place potatoes in a pot of cold water and heat until boiling. After the pot has been boiling for 10 minutes, remove from the heat. Allow the potatoes to cool slightly in the cooking water before draining.
In a large bowl combine mayonnaise, onion, celery, sugar, red wine vinegar and mustard. Season with salt and pepper. Add the warm potatoes and stir to coat.
Gently fold the hard boiled egg through the salad and add additional seasoning if required.