Preheat the oven to 180°C / 350°F / Gas mark 4.
Line 2 baking sheets with grease proof paper and set aside.
Combine the flour, baking powder, spice and sugar in a large bowl, then mix well.
Stir in the eggs and zest until the mixture starts forming clumps, then bring the dough together with your hands.
Keep kneading until no floury patches remain.
Add the fruit and nuts, mixing well.
Turn the dough out onto a lightly floured surface and divide into 4 pieces.
With lightly floured hands, roll each piece into a sausage shape about 30cm long.
Place 2 on each tray, spaced apart.
Bake for 25-30 minutes until the dough has risen, and feels firm.
Remove from the oven, transfer to a wire rack until cool enough to handle.
Turn down the oven to 140°C / 275°F / Gas mark 1.
Using a bread knife, cut the sausage shapes into slices about 1cm thick on the diagonal, then lay the slices flat on the baking sheets.
Bake for another 30 minutes turning half way through until golden and dry.
Tip onto a wire rack to cool completely, then store in an airtight tin for up to one month, or wrap as gifts.