D was empowered under legislation to allow cinemas to open on Sundays “subject to such conditions as the authority think fit to impose”. He allowed P’s cinema to open on Sunday provided that no children under 15 are admitted. P challenged the condition as ultra vires but CA held that the decision was not unlawful.
Lord Greene MR: “If a decision on a competent matter is so unreasonable that no reasonable authority could ever have come to it, then the courts can interfere. That, I think, is quite right; but to prove a case of that kind would require something overwhelming” and this was not the case on the facts. The question is not what the court considers unreasonable (that would be to substitute the judgment of the court for that of DM) but what no reasonable body would consider reasonable.