Photograph: Martin Poole
Grease and line a 20cm square tin with baking paper. Break up the spiced orange, dark and milk chocolates into small pieces and place in a heatproof bowl with the butter and syrup. Sit the bowl over a pan of barely simmering water and heat gently until melted. Remove from the heat and stir to combine.
Put the biscuits into a food bag, seal and break into pieces with a rolling pin. Roughly chop the pistachios. Add three quarters of the crushed biscuits, the pistachios, cherries, marshmallows and all the ginger to the chocolate and mix well to coat.
Spoon into the prepared tin, scatter over the remaining biscuits, cherries, pistachios and marshmallows, and press. Chill for 1-2 hours, or until firm. Lift out of the tin and cut into squares.
Get ahead: make up to 2 days ahead and chill. Store in an airtight container in the fridge for up to a week.