Preheat the oven to 140°C gas 1.
Place the cranberries, prunes, cherries, currants and dates in a large saucepan with the stout and set over a high heat. Bring to the boil and allow to bubble away for 1 minute, then reduce to a simmer and leave for about 5 minutes.
Remove from the heat and add the brandy, sugar and butter, and stir with a wooden spoon until well incorporated. Stir in the eggs and flour, along with the walnuts, zests, mixed peel and mixed spice. Mix well together, then scoop into the prepared tin. Gently cover the cake tin with the circle of foil, having cut a small hole in the centre: this will protect the top of the cake from burning.
Place the tin on a baking sheet and transfer to the oven. Bake for 3 1/2 - 4 hrs, or until the cake has stopped making a gentle bubbling, crackling sound. Remove from the oven and leave to cool completely in the tin before turning out on to a cake stand.
Decorate as you wish.