Crush the biscuits in a food processor or by putting them in a plastic bag and hitting them with a rolling pin until they are gravel-like, but not too powdery.
Melt the butter, cocoa, sugar and golden syrup together in a saucepan. Add the raisins and chopped pecans, then stir in the biscuit bits.
Line the tin with cling film then pour in the biscuit m