Preheat oven to 190 degrees C. Sift together the flour, bicarb soda and salt into a small bowl; set aside.
In a large bowl, cream together the butter, margarine, white sugar and brown sugar until smooth. Beat in the eggs one at a time then stir in the vanilla and milk. Gradually stir in the sifted ingredients using a wooden spoon. Finally, mix in the chocolate chips and crystallised ginger. Use two spoons to drop biscuit dough 5cm apart onto a baking tray.
Bake on the middle rack of the preheated oven for 12 to 15 minutes. The biscuits should be golden brown on the sides and the top should have lost its shine. Allow to cool on the baking tray for a few minutes before removing to a wire rack to cool completely.