Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, stir together the flour, rolled oats, shredded coconut, brown sugar, and salt. Break up any lumps of brown sugar with your fingers or a spoon.
In a small saucepan over low heat, melt the butter with the golden syrup, stirring until smooth. Remove from the heat.
Stir the baking soda into the boiling water in a small heat-safe cup. It will foam. Immediately stir this mixture into the melted butter and syrup.
Pour the warm butter mixture over the dry ingredients. Stir until no dry flour remains and the mixture holds together when pressed.
Scoop rounded tablespoons of dough onto the prepared baking sheets, leaving about 2 inches (5 cm) between each mound. Gently flatten each one slightly with the back of a spoon.
Bake for 10 to 12 minutes, rotating the pans halfway through, until the biscuits are deep golden at the edges. Bake closer to 10 minutes for a slightly chewier center or closer to 12 minutes for a crisper biscuit.
Let the biscuits cool on the baking sheets for 5 minutes, then transfer them to a wire rack. They will firm up and become crisper as they cool.