Preheat the oven to 180ºC, fan 160ºC, gas 4. In a bowl, beat together the butter and sugar until creamy, then stir in the bicarbonate of soda, golden syrup and egg yolks. Sift in the flour, ginger and cinnamon. Using your hands, bring the mixture together to form a ball.
On a lightly floured surface, roll the dough out to a thickness of ½cm. Use a gingerbread man cutter to stamp out 16 biscuits. Transfer the biscuits to the lined baking tray and bake for 10-12 minutes, then cool on wire rack.
Mix the icing sugar with the hot water. Spoon into a piping bag and cut a small hole from the end, or use a small nozzle. Pipe onto the cooled biscuits to create skeletons. Break off a few limbs and heads and ice with the red icing so they look bitten off. Leave to set and then serve.