1. Cream the butter, oil and sugar. Mix the flour and baking powder.
2. Beat one egg and half of the flour into the butter mixture, then the other egg and the rest of the flour. Mix in the chopped fruit and the walnuts.
3. Put into a greased Swiss roll tin and bake for 20 minutes at 375°F (190°C) gas mark 5. When cold, cut into slices.