1. Put the flour, sugar, baking powder, bread soda, margarine, orange juice and egg into a bowl and mix well until smooth. Fold fruit into cake mixture. Transfer to a greased and base lined 2lb (900g) loaf tin. Bake in a preheated oven at 350°F, 180°C, Gas 4 for 20-25 minutes.
2. Remove from oven, sprinkle on the demerara sugar. Return to the oven and bake for a further 30-40 minutes or until a skewer, when inserted into the loaf, comes out clean. Leave in tin for 5 minutes, then cover with kitchen paper on a wire rack. Turn over carefully to avoid spilling coating. Leave to cool.

Notes:

Toss the prepared fruit in flour until well coated on all sides - this helps ensure an even distribution in the cake.
Any pineapple rings that are over can be chopped and added to the topping mixture