Pre-heat your oven to 180°c (160°c for fan assisted oven or Gas Mark 4). Grease a square 8 inch baking tin with butter/margarine and dust it with a little flour too. Set aside.
Place the dates and water into a small pan and bring to a boil. Turn down the heat to a simmer for a minute before removing from the heat and setting aside to steep.
In a large bowl, cream together the butter/margarine and sugar until it is well mixed. Add the syrup, treacle, eggs and vanilla extract and mix until combined.
Gently sift in the flour and fold together to create a batter. Set aside.
With a hand blender, mix the date and water mixture (alternatively, mash with a potato masher), then add the bicarbonate of soda and mix. The mixture will have a frothy consistency - this is normal.
Whilst the date mixture is still warm, add it to the batter and mix to combine before pouring the completed batter mixture to your pre-greased baking tin.
Bake in your pre-heated oven for 30-35 minutes until the pudding is firm. Once cool enough to touch, turn the pudding out onto a wire rack to cool completely. Once completely cool, use a knife to loosen the edges from the tin and cut into 9 individual portions. See notes for instructions on making ahead and storing/freezing.