1. Soak the Fruits: Combine raisins, currants, prunes, cherries, and candied peel in a bowl. Add grape juice and orange juice. Cover and refrigerate overnight, stirring occasionally.
2. Prepare the Fruit Mixture: Blend or finely chop the soaked fruits into a thick mixture. Set aside.
3. Prepare the Oven: Preheat the oven to 150°C (300°F). Grease a deep 8-inch cake tin and line it with baking paper.
4. Cream Butter and Sugar: In a large bowl, beat softened butter and brown sugar until light and creamy.
5. Add the Eggs: Add the eggs one at a time, beating well after each addition. Stir in vanilla extract and orange zest.
6. Combine the Dry Ingredients: In a separate bowl, sift together flour, baking powder, salt, mixed spice, cinnamon, and nutmeg.
7. Make the Batter: Gradually fold the dry ingredients into the butter mixture. Add the blended fruit mixture and burnt-sugar syrup. Mix until evenly combined.
8. Fill the Cake Tin: Pour the batter into the prepared tin and smooth the surface. Gently tap the tin to remove large air pockets.
9. Bake the Cake: Bake for approximately 1 hour 30 minutes to 2 hours. Check the centre with a skewer; it should come out without wet batter. If the top browns too quickly, cover loosely with foil.
10. Cool Completely: Remove the cake from the oven and let it cool in the tin for about 20 minutes. Transfer to a wire rack and allow it to cool completely before slicing.
11. Serve: Cut into small slices and serve with tea, coffee, or as part of a festive dessert table.