Preheat the oven to 180°C/160°C fan/350°F/gas mark 4. Grease a 2lb loaf tin (approx 11.5 x 21.5 cm / 4.5 x 8.5 in) and line it with baking parchment.
Sift together the flour, bicarbonate of soda, ginger, cinnamon, mixed spice, nutmeg, star anise and salt in a large bowl.
If you are adding the crystallised (candied) ginger, stir two-thirds of it into the dry ingredients, saving the rest to scatter over the top of the cake.
Place the butter, golden syrup, treacle and brown sugar in a saucepan over a low heat, stir until melted then whisk in the milk.
Pour the butter mixture into the dry ingredients. Stir with a balloon whisk until no dry lumps remain. The batter will be very liquid.
Pour the batter into the loaf tin and scatter over the reserved ginger.
Bake for about 50 minutes until a skewer inserted into the centre comes out clean.
Leave the cake to cool in the tin for about 30 minutes then carefully turn it out onto a wire rack and leave to cool completely.