In a small bowl, pour boiling water over dates and set aside to cool. Preheat oven to 170 C / Gas 3. Grease a 26cm square tin.
In a medium bowl, cream together the margarine and caster sugar. Add eggs, one at a time, beating after each addition. Add the dates, including any water; mix well. Sieve together the flour, cinnamon, nutmeg and bicarbonate of soda; stir into the date mixture. Then stir in the nuts.
Spread the mixture evenly into the prepared tin and bake for 45 minutes in the preheated oven. When cool, cut into bars and roll each bar in icing sugar.