Line a 2lb loaf tin with a double layer of grease proof paper. Melt the butter, syrup and chocolate in a pan over a low heat. Stir to make sure all the ingredients are well mixed together. Add the biscuits and maltesers. Stir well. Transfer to prepared tin. Level it on top and press down well to avoid air gaps. Allow to cool. Wrap completely in greaseproof paper and store in the fridge.