Heat butter in a large saucepan. Add bacon and leeks and cook over medium-high heat for 1-2 minutes. Add potatoes and stir to combine.
Pour in GRAVOX Vegetable Stock and 3 cups of water. Bring to the boil, reduce heat and simmer for 20 minutes.
Place GRAVOX Sauce Mix in a heatproof jug, pour in remaining water and stir vigorously until smooth. Add to soup and season with SAXA Salt and Pepper and parsley.