Preheat the oven to 180 degrees or 160 degrees if using a fan oven. Grease a loaf tin about 18-20cm in diameter, with a little butter. You could also use a round cake tin or square baking dish.
Put the dates in a medium bowl and cover with 125ml of boiling water. Leave the dates to soak for 10-15 minutes while preparing the rest of the pudding ingredients.
In a large bowl, beat together the soft butter and brown sugar until soft and creamy. Add the eggs one at a time, beating well between each addition.
In a separate bowl, sift the self-raising flour together with the cinnamon, ginger and nutmeg/allspice and set aside.
Put the softened dates into a food processor with the soaking water and blend to a smooth purée. Add the date puree to the butter, sugar and egg mix along with the treacle and beat until well combined.
Add half of the sifted flour and spices and fold through gently before adding the remaining flour and mixing until the batter is just combined.
Pour the batter into the prepared tin and bake in the preheated oven for 30-35 minutes until cooked through or a skewer inserted into the centre comes out clean.