Line and grease a seven-inch round cake tin. Beat butter and sugar together until light and creamy. Beat in the egg yolks, one at a time, then one tablespoon of the flour. Stir in marmalade, peel, orange rind and water. Fold in the remaining flour. Whisk the egg whites until just stiff and fold into the cake mixture. Turn into the prepared tin and bake at 350°F, 180°C, gas mark 4 for one and a quarter hours until risen and firm to the touch. Cool. Icing: Blend icing sugar with sufficient orange juice to give a stiff coating consistency. Pour over cake and allow icing to trickle down sides. Leave to set. Cut slices of crystallised orange in half and use to decorate the top.