Place a heavy-based saucepan over medium coals (or a medium heat), combine the sugar, golden syrup, butter and salt and stir over a low heat until melted.
Bring to a boil and simmer for 6 minutes.
Remove from the heat, add the chipotle and then the bicarbonate of soda. The caramel will froth up.
Stir well and pour over the popped popcorn and mix to coat.
Spread onto a baking sheet and bake at 100°C, gas mark ¼, for 30 minutes, stirring after 15 minutes.
Allow to cool before serving, or store in an airtight container.