Cream the butter and sugar until light and fluffy. Beat in the egg and stir in the treacle. Sift the flour, ginger, spice and salt together and stir into the creamed mixture. Dissolve the bicarbonate of soda in the milk and stir into the cake mixture. Add the fruit and mix well. Turn into a 20cm (8 inch) round cake tin lined with greased greaseproof paper and bake in a moderate oven (170C, 160ºC , gas mark 3) for 1 hour or until cooked.