Heat oven to 180°C/ 160°C fan. Line a 2lb loaf tin with baking parchment. In a bowl, combine the dry ingredients. Flour, Bicarbonate of soda, mixed spice, ground ginger, ground cinnamon, nutmeg and salt.

Place the coarsely grated carrots in a tea towel and squeeze over the sink and remove as much liquid from the carrots as possible. Add the carrots to a jug or bowl, pour in the oil. Crack in the eggs and add the sugar and orange zest, mix until combined. If using raisins or walnuts, they can be stirred into the batter at this stage.

Pour the batter into the prepared loaf tin and bake for 55 - 60 minutes until a skewer inserted comes out clean. Allow to cool completely in the tin.

In a large bowl, beat the butter with an electric mixer until pale and fluffy. Add the icing sugar a third at a time until all incorporated. Add the vanilla and cream cheese and continue to beat until almost white and fluffy.

Remove the cake from the tin and peel away the parchment paper. Fill a piping bag fitted with a fluted nozzle with icing and pipe the icing on top of the loaf or alternatively spread generously with a knife or spatula. Sprinkle with chopped walnuts if desired.