Bash or process half of the biscuits into crumbs and the other half into small chunks about 1 cm.
In a saucepan melt the butter, sugar, cocoa, golden syrup together until well mixed.
Put the biscuits, nuts and fruit in a large bowl, pour over the melted mixture and blend well.
Grease a tin similar to 19X33 cm and spread the mixture into an even layer and refrigerate for 20 minutes until set.
Melt the milk chocolate over a bain marie or in the microwave and pour over biscuit base to cover.
Melt the plain chocolate and pour thin lines one way over the milk chocolate then use a cocktail stick or a skewer to drag through the chocolate from alternate ends.
Allow the chocolate to harden before cutting into squares.