The invention relates to a membrane and method for its manufacture, the method including the steps of (1) providing of an ultrafiltration membrane, and (2) modification of the resultant ultrafiltration membrane to provide an asymmetric porous ion exchange membrane. The modification of the ultrafiltration membrane is typically carried out by (i) exposing said ultrafiltration membrane to a first functional reagent to provide a cross-linked ultrafiltration membrane, and then (ii) exposing said cross-lined ultrafiltration membrane to a second functional reagent to introduce positive charged groups to produce an anion exchange membrane.