Heat the oven to 180C/350F.
Mix together the flour, salt and bicarbonate of soda.
Cream the butter, sugar in another bowl until pale and fluffy. Add the eggs and flour alternately a little at a time.
Stir in the bananas and chopped walnuts.
Pour into a prepared loaf tin. Cook for about 11/4 hours until the sponge bounces back when pressed gently or use a skewer to test that it is cooked through. Turn out onto a wire rack to cool.