Pre-heat your oven to 170°c (150°c for fan assisted oven, Gas Mark 3-4 or 325°F) and line a couple of baking sheets with greaseproof paper. Set aside.
In a large bowl, cream together your butter/margarine and sugar, until light (in texture - the colour will remain darker due to the brown sugar) and fluffy. Add your golden syrup and stir through to combine.
Sift in your flour, bicarbonate of soda (baking soda), ginger and cinnamon. Mix your dry and wet ingredients together to make a stiff dough - you will probably need to use your hands!
Gently knead the dough together, before rolling with a rolling pin on a well floured surface, to around 0.5-1cm thick. Using the gingerbread house template, cut out the walls and roof shapes (6 pieces in total) and transfer to your pre-lined baking sheets, leaving a little space between them. Using a large palette knife to support the pieces as you move them will prevent them from breaking.Knead together any off-cut before re-rolling the dough, and use any excess to cut out small biscuit shapes to decorate your house.
Bake your gingerbread biscuits in your pre-heated oven for 15-20 minutes. When they are golden and dry looking, remove from the oven to cool. Be careful not to overbake your biscuits - this can happen quickly due to the presence of golden syrup in the dough.
Once baked, remove from the oven and gently push - not cut! - the edges of the biscuits with a large palette knife (or just a normal knife) to help straighten them out a little - they may have spread and curved a little whilst baking, this helps correct this. Allow the biscuits to cool completely on the trays - they will continue to harden as they cool, so don't be tempted to try and lift them before they are completely cool.
When cold, you can start to construct your gingerbread house. Mix 200g [half] of the icing sugar (powdered sugar) with 1-2 tbsp of boiling water, so you have a thick sticky icing, which is still spreadable but not runny. Start by attaching your walls together - if you can have someone help you hold the walls upright, this will help; alternatively you can prop them up with some mugs or drinking glasses. Be generous with the amount of icing you use, and don't worry about being overly neat - you can easily cover it with some decor. Once you have your walls upright, stick on the roof pieces with plenty icing too. Allow your gingerbread house to dry before decorating.
Once the icing has dried, you can start decorating your gingerbread house. Mix the remaining 200g of icing sugar (powdered sugar) with 1-2 tbsp of water until it is a piping consistency. You can use a piping bag, or simply drizzle/spoon onto your house. Be creative and have some fun!
Notes
For full Ingredients explanations and substitutions, please see the Ingredients section above.
For lots more tips & tricks for success, please see Granny's Top Tips section above.
For free-from substitutions to make this a vegan, dairy-free, nut-free, egg-free...gingerbread house, see the Free-from section below.