“A policy must not be so inflexible that it cannot accommodate the range of situations to which it has to apply, nor must it be so rigid that it does not allow for exceptional cases; otherwise it will result in an unlawful fetter on discretion.” (R v Secretary of State for the Home Department ex p Venables and Thompson  3 ALL ER 97).
In some circumstances, a decision-maker may improve certainty and administrative efficiency by adopting a policy setting out how it deals with a particular type of decision (e.g. how it determines licence applications).
The policy itself must be lawful; it must comply with all relevant requirements set out in legislation and with the public law principles set out in this guidance (e.g. must be reasonable).
The decision-maker may not ‘fetter’ its discretion by applying a policy too rigidly – without allowing for exceptions or allowing an applicant to argue that the policy should be departed from in a particular case.