Preheat the oven to 160C/320F fan-forced. Grease and line the bottom of a round spring-form tin.
Beat the oil, sugar and eggs together in the bowl of an electric mixer until thick and creamy.
Take the bowl off the stand and using a wooden spoon, mix through the carrot, walnuts and sultanas.
Stir through the rest of the dry ingredients after sifting them.
Pour the batter into the tin and bake for 1h 15 minutes or until a cake tester comes out clean.
When the cake is done, remove it from the oven and leave it in the tin for 5 minutes before transferring to a wire rack to cool completely.
To make the icing, blend the cream cheese and low fat spread until smooth and creamy. Add the lemon juice then gradually add the icing sugar until you reach the desired consistency.
Give the cake a crumb layer of icing and leave to set.