Blitz the digestive biscuits in a food processor to a fine crumb or crush in a sealed plastic bag with a rolling pin. Divide into two and set aside.
In a food processor or large bowl mix together the cream cheese and peanut butter until well combined. Mix in the icing sugar, cocoa powder and half of the crushed biscuits. Beat together until smooth.
Place in a sealed container in the fridge for a minimum of 3 hours. Overnight works well too.
When ready roll heaped teaspoons of the mixture between your clean hands to form a ball. You should get about 24 balls in total.
Roll each ball in the remaining digestive biscuit crumbs. Coat completely. Transfer the coated balls into an airtight container and refrigerate until serving. They will keep for 3-4 days perfectly well in the fridge.