Heat the oil in a large saucepan and cook the leek for 2 minutes. Add the water and the stock cubes. Bring to the boil and cook for a further 5 minutes.
Add in the garden peas and cook for another 2 minutes. Put three-quarters of the basil into the soup, turn off the heat and puree with a hand blender until smooth.
Divide the soup over 4 bowls and sprinkle with the crumbled cheese and the rest of the basil to serve. Season with freshly ground pepper.