Shadowy Regime

What is the point of having tax legislation passed by Parliament the terms of which are relied on by taxpayers if there is a shadowy regime of taxation by policy decree represented by this practice of ex gratia relief? You pay the normal tax but then you get it back. How many taxpayers know of that and the topics for which it has been granted. Taxpayers should be able to look up the lists where ex gratia has been granted before they enter into a transaction.