The first factor is the nature of the policy. There is a spectrum of different kinds of policy. It ranges from the most formal to the most informal. The second factor is the deference that the Court ought to pay to the decision-maker in deciding whether uit had good reason to depart from its policy. Some level of weight should be attached to the judgment of a specialist experienced decision-maker. The required deference is also on a spectrum.
There is no bright line rule that good reasons can be reviewed only if they are irrational or unreasonable. In considering whether a decision-maker had good reason for departing from a policy one considers first where on the spectrum of policies the relevant one lies and where on the spectrum of appropriate deference the particular type of decision lies.
So held in R ( DUKE OF SUSSEX ) v SSHD ( 2025 ) EWCA Civ 548 at paras 62-69 inc.