Sieve together the flour, salt and baking powder. Cream the butter and sugar. Add the eggs to the creamed mixture alternately with some of the flour mixture. When the eggs and flour have been incorporated, add the sultanas, currants, lemon rind and mixed peel, stirring but not beating. Stir in the brandy. Put into a greased eight inch tin and bake at 350°F, 180°C, gas mark 4 for one and three quarter hours.