Line a large tupperware with tin foil and grease with oil.
Mix caster sugar and golden syrup in a deep saucepan and stir over a gentle heat until the sugar has melted.
Once completely melted, turn up the heat a little and simmer until you have an amber coloured caramel, then as quickly as you can turn off the heat, tip in the bicarbonate of soda and beat in with a wooden spoon until it has all disappeared and the mixture is foaming. Scrape into the tin immediately and leave it to set for about 1 hr.
Melt ⅓ of the milk chocolate in a bain marie and pour over the honeycomb in the tin - this will be the bottom of your crunchie bar, then set aside to cool completely.
Carefully remove the honeycomb from the loaf tin and place on a wire rack set over a baking sheet then melt the remaining chocolate and pour over the honeycomb bar.
Set aside to cool again and when fully set slice/bash into pieces to eat!