Pour the water and vinegars into a saucepan, and pour in the salt and the sugar.
Bring it to a simmer, and stir it all together until everything has dissolved.
Smash the garlic under the flat of a knife and throw it in, as well as the chilli, then bring it to a boil.
When boiling, spoon in the golden syrup and stir well, then lower the heat to a hearty simmer. This will give it a lovely caramel flavour.
Reduce until roughly half the liquid has evaporated, then leave to sit for a while.
When it has stopped steaming (you don't want chilli steam in your eyes), sieve it through a fine cloth, then return it to the pan.
In a little bowl or cup, add a tablespoon of the sauce to a teaspoon of cornflour and stir until a paste is formed.
Add this to the rest of the liquid and bring to a boil one last time, stirring enthusiastically.
While still hot, pout into a bottle.
Allow to cool, then pour on everything.