They can add a number simply by dialling 1572 after receiving the call
OK, something the victim can do to register with them, as opposed to some third-party. This is progress.
What we really need is a version of that that applies some kind of penalty on any caller who collects more than a handful of 1572s. Say, £1 per spam call, collected by BT/phoneco as in normal billing and going to Good Causes (in the manner of a Lottery).