Preheat oven to 325 degrees F (160 degrees C). Line one 8x3 inch round cake tin with parchment paper.
In a medium saucepan, combine mixed fruit, cherries, citrus peel, walnuts, sugar, butter, milk, mixed spice, and baking soda. Bring to a boil, and simmer for 5 minutes. Let the mixture cool to room temperature.
Stir in flour and eggs. Pour into the prepared pan. Wrap outside of pan with brown paper or newspaper.
Bake at 325 degrees F (160 degrees C) for 40 minutes, then reduce temperature to 300 degrees F (150 degrees C), and continue to baking cake for 1 1/2 hours. Remove cake from oven, and allow to cool in the tin for 5 minutes, then turn it out onto a cooling rack, remove paper, and cool completely. Cake can be stored for up to 6 months wrapped in foil and in an airtight tin.