In a large bowl, mix together the plain flour, baking powder, ginger, cinnamon, allspice and orange zest.
Rub the butter into the flour mixture until the mixture resembles breadcrumbs. Stir in the sugar. Add the golden syrup and treacle to the mixture, then add half of the beaten egg, using a table knife or your hands to bring the mixture to a dough. If the dough is dry and there are still a lot of crumbs at the bottom of the bowl, add a little more egg, a drop at a time, until the mixture begins to cohere. When the mixture starts coming together, gently knead to form a soft dough, then cut in half, wrap each half in cling film and place in the fridge for a minimum of 1 hour.
Preheat the oven to 180C/160Fan/350F. Grease and line a couple of large baking trays.
Remove the dough from the fridge. Sprinkle a work surface with some flour and place one half of the dough on top. Sprinkle a little more flour on your rolling pin and roll the dough out evenly, giving the dough a quarter turn after every 2 rolls to make sure it isn't sticking to the work surface. If it is, add a little more flour to your surface.
When the dough is around the thickness of a £1 pound coin, cut out your shapes and transfer to your lined baking trays.If you're planning to hang the biscuits on the Christmas tree, you'll need to cut out a hole at the top for your ribbon. Just bear in mind the hole will close up if it's too small - I use the pointy end of a small icing nozzle.
Bake for 18-20 minutes or until cooked through. Leave on the baking trays for 5-10 minutes before transferring to a wire rack to cool completely.
Make up the royal icing according to packet instructions and decorate the biscuits however you like - you can get fancy and use a piping bag for pretty patterns, or simply use a teaspoon to drip the icing on the biscuits and cover in Christmas sprinkles!