Line the loaf tin with oiled greaseproof paper. Briefly dip the biscuits in the rum and line the bottom and sides of the tin facing the rounded pale side inwards. Keep some in reserve for the top. In separate double saucepans melt the two chocolates. Take off the heat and Stir in the cold cream. Pour the chocolate mixtures into the waiting tin alternating the dark and white to form layers. Allow to set for at least an hour and a half in a cold fridge. Turn out and cut into thickish slices decorated with frosted fruits, mint leaves and a dusting of icing sugar.