Line and grease a 20 x 14cm cake tin with baking parchment. Preheat oven to 180°c. Cream butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition. Add vanilla essence.
Fold in the sifted ingredients gently. Stir in carrot, sultanas, currants and walnuts. Turn the mixture into prepared pan. Bake in preheated oven at 180°c for 40 minutes and 160°c for 10 minutes.