In a large bowl, mix together the raisins, sultanas, currants, mixed peel, brown sugar, breadcrumbs, suet, mixed spice, nutmeg, and flour.
In a separate bowl, beat the eggs and stir in the stout, black treacle, lemon zest and juice, and grated apple.
Combine the wet ingredients with the dry ingredients, mixing thoroughly until everything is well combined.
Spoon the mix into a greased pudding basin and level the top. Cover with a double layer of baking parchment and a layer of foil, securing with string.
Steam the pudding in a large saucepan or steamer for 7 hours, ensuring the water remains halfway up the side of the basin.
Allow the pudding to cool in the basin, replace the parchment and foil if needed, and store in a cool, dry place to mature.
On Christmas Day, steam the pudding for a further 2 hours before serving with your choice of accompaniment.