Legal unreasonableness back in season — with mixed success

Key Points:

Traditionally, the ground of legal unreasonableness was only available for a conclusion that was "so unreasonable that no reasonable authority would ever consider imposing it" (Associate Provincial Picture Houses Ltd v Wednesbury Corp [1947] 1 KB 223). It was regarded as an exceptional ground that was not easily satisfied.

However, the decision of the plurality of the High Court in Minister for Immigration and Citizenship v Li expanded Wednesbury unreasonableness. It is no longer a ground which would only succeed in exceptional circumstances, rather "[u]nreasonableness is a conclusion which may be applied to a decision which lacks an evident and intelligible justification".