Grease a 9×5-inch (2 lb) loaf pan and preheat the oven to 325°F (163°C).
Place the raisins, sultanas, dried currants and candied lemon and orange peel in a bowl.
Pour the very hot strong black tea over the fruit, stir to combine, cover and leave to soak overnight; if there is excess liquid in the morning reserve 2–3 tablespoons to brush on the finished loaf.
In a large bowl or the stand mixer bowl, whisk together the all-purpose flour, baking powder, salt and mixed spice until evenly combined.
Add the soaked fruit with any remaining (not reserved) juice, the dark brown sugar, softened butter and lightly beaten egg to the dry ingredients.
Use the paddle attachment to mix into a soft dough resembling cookie dough; if it seems too dry, add a little melted butter or a small amount of extra beaten egg yolk.
Spoon the batter into the prepared loaf pan and smooth the top with the back of a spoon or your fingers.
Bake for 70–85 minutes, until a toothpick or skewer inserted into the center comes out clean.
Immediately after removing from the oven, brush the reserved fruit-soaked tea over the hot loaf if you reserved any, then cool in the pan for a few minutes before transferring to a wire rack to cool completely.
Slice to serve, traditionally with butter and a cup of tea.