In R (ZK) v Redbridge London Borough Council (2019) EWHC 1450 (Admin) Swift J held, at paragraph 37, that the existence of an unacceptable risk of illegality in the operation of a policy is capable of giving rise to a ground of judicial review challenge, whether or not the arrangements give rise to an unacceptable risk of unfairness. The principle (paragraph 38) is an applicable standard to judge substantive policies too.
Such capability is to be assessed (paragraph 39) “realistically and pragmatically”.