“The importance of Anisminic is that it established that there was a single category of errors of law, all of which rendered a decision ultra vires….” 61. The statutory scheme does not provide any mechanism for challenging the lawfulness of the kind of decision that was in issue in Lumba: an (unlawful) decision to detain where there had been a (lawful) decision to make a deportation order/the making of a (lawful) deportation order. The lawfulness of such a decision can be challenged only by way of judicial review. In sharp contrast, Parliament has established a comprehensive statutory scheme for determining the lawfulness of a decision by the Secretary of State to make a deportation order. The Secretary of State may not make the order until an appeal against the decision to make it has been “finally determined” (see paragraph 33 above). In order to give effect to the statutory scheme there is a very strong case for treating the Tribunal’s decision on an appeal under section 82(1) as determinative (subject to any appeal to the Court of Appeal) of the issues as between the parties to the appeal in order to ensure finality in litigation and legal certainty. 62. The law, particularly in this field, is constantly evolving, as shown by the number of reported cases. The fact that a decision by the Court of Appeal or the Supreme Court in a later case, perhaps many years later, may, with the benefit of hindsight, make it clear that a Tribunal’s decision in an earlier case to allow or dismiss an appeal against a decision to make a deportation order was made on an erroneous legal basis is not a ground for re-opening the earlier decision by the Tribunal. It would frustrate the operation of the statutory scheme if the Secretary of State was not able to rely upon the Tribunal’s decision, dismissing an appeal, once time for applying for permission to appeal against the decision had expired, as a lawful basis for making a deportation order. “The importance of Anisminic is that it established that there was a single category of errors of law, all of which rendered a decision ultra vires….”
"an indispensable foundation upon which to decide what is the law and its application to individual cases. It provides at least some degree of certainty upon which individuals can rely in the conduct of their affairs, as well as a basis for orderly development of legal rules."