Non-bake chocolate 'cake'

Having committed myself to baking for a charity cake stall this weekend, I looked through my old recipe file and came across 'Mum's non-bake chocolate cake' and decided that it was within my limited baking abilities. It consists of a cocoa/margarine/water/icing sugar mixture, binding mixed fruit and broken biscuits, which solidifies in the fridge. Made in honour of my mum!