Unreasonableness as a Ground of Judicial Review

‘Irrationality’ is the second of the three grounds for judicial review identified by Lord Diplock in the seminal case Civil Service Unions v Minister for the Civil Service (‘GCHQ’). In that case Lord Diplock characterised the ground as ‘a decision which is so outrageous in its defiance of logic or of accepted moral standards that no sensible person who had applied his mind to the question to be decided could have arrived at it’.

Today the courts often favour the language of ‘unreasonableness’ over ‘irrationality’, though the two terms continue to be used interchangeably.

This Practice Note will address the central features of reasonableness as a ground of judicial review:

1. •

   the development of reasonableness review,

2. •

   the Wednesbury standard of reasonableness,

3. •

   the two limbs of unreasonableness,

   1. ◦

      unreasonable approach/route,

   2. ◦

      unreasonable outcome/terminus,

4. •

   adjustments to the Wednesbury standard of reasonableness,

   1. ◦

      ‘super Wednesbury’,

   2. ◦

      sub Wednesbury’,