Heat the oil in a large saucepan over a medium heat for 1 minute. Add the popcorn and cook until the kernels start to pop, then cover and cook for 5–7 minutes, shaking occasionally, until the kernels have stopped popping. Remove from the heat.
Meanwhile, place the sugar and measurement water in a medium saucepan and bring to the boil, then reduce the heat and simmer until the mixture turns golden brown. Remove from the heat and add the butter, bicarbonate of soda and chilli powder.
Pour the caramel over the popcorn and stir well to coat, then spread out on a baking sheet lined with nonstick baking paper. Place in a preheated oven, 150°C (300°F), Gas Mark 2, for 10 minutes until dried out. Allow to cool for a couple of minutes before serving.