GROUNDS OF JUDICIAL REVIEW IV: IRRATIONALITY
In this chapter, we examine the principles governing the ground of review which Lord Diplock, in the GCHQ case (R v Minister for the Civil Service ex p Council of Civil Service Unions (1985)), called ‘irrationality’. In the broadest of terms, we can characterise this head as involving review of the substance of the decision (or rule) challenged; in other words, review (however limited) of the merits of the decision or rule. Judges have, in the past, been very reluctant to concede that this ground of review does involve a judgment of the merits of the decision; indeed, to a cynic’s eye, the courts appear sometimes to have almost deliberately declined to clarify the basis upon which they do or do not intervene. As we shall see, one important task in this chapter is to distinguish what judges say from what they actually do.