Break the popping candy bars into small pieces and chill in the fridge. Line a 23cm square tin with baking paper.
Put the digestive and ginger nut biscuits in a large freezer bag, then bash them with a rolling pin until broken - you want a mix of small biscuit pieces and crumbs.
Break the milk and dark chocolate into squares and put in a large heatproof bowl with the butter and golden syrup. Place the bowl over a pan of simmering water, making sure the base of the bowl doesn't touch the water, leave until melted.
Remove the bowl from the pan. Stir in the biscuits, sultanas, cherries and marshmallows. Spread half the mixture in the lined tin.
Place the popping candy pieces on top, distributing them evenly. Cover with the rest of the biscuit mixture and level the top.
Chill in the fridge for at least 2 hours, then cut into small squares, to serve.