IN a medium bowl, cream the butter and sugar in a bowl until well combined. Add the eggs one at a time and beat until they are combined, do not overbeat. Dissolve the soda in hot water, and add to the dates and raisins. Stir the date mixture into the egg mixture, then stir in the sifted dry ingredients. Finally, mix in the walnuts.
Drop level tablespoons of the mixture onto greased oven trays, about 2cm apart. Bake for about 10 minutes, or until browned. Remove from oven, and allow to cool slightly before transferring to a wire rack to fully cool.