Dickinson – Court of Appeal of England and Wales states that Revenue must not let the application of its internal policies preclude the exercise of its statutory discretion

In the course of considering whether a determination by HMRC to issue advance payment notices to taxpayers before their appeals of tax assessments were heard amounted to an unlawful abuse of power (it did not), McCombe LJ discussed the tension between the desirability of HMRC developing and applying policies consistently while at the same time being mindful of the need to exercise its discretion. In this regard, he quoted with approval an earlier statement that

One aspect of the duty of fairness is that, in general, a decision- maker may not fetter his discretion. However, it is well established in public law that a decision- maker may formulate a policy to enable him to exercise a discretion consistently provided that it is not applied so rigidly that it precludes the proper exercise of discretion in each case.

And then stated:

The simple rule is, as Arden LJ said, the internal policy must not preclude a proper exercise of the statutory discretion in each case.

Neal Armstrong. Summary of Dickinson & Ors v Revenue and Customs [2018] EWCA Civ 2798 under ETA s. 315(3).