Kruse v Johnson [1898] 2 QB 91 is a UK administrative law case, concerning the judicial review of decisions by public bodies.

According to him, if rules under authority of an Act of Parliament, ... were found to be partial and unequal in their operation as between different classes; if they were manifestly unjust; if they disclosed bad faith; if they involved such oppressive or gratuitous interference with the rights of those subject to them as could find no justification in the minds of reasonable men, the Court might well say, “Parliament never intended to give authority to make such rules; they are unreasonable and ultra vires.

"Kent County Council made a bylaw, under authority of the Local Government Act 1888 section 16, that nobody, after being requested to stop by a constable, could play music or sing within 50 yards of a dwelling house in a public place or highway.

Lord Russell CJ, giving the court's leading judgment, held the bylaw was valid on the ground that it was not unreasonable, because it did not have a discriminatory impact on the population.

If, for instance, they were found to be partial and unequal in their operation as between different classes; if they were manifestly unjust; if they disclosed bad faith; if they involved such oppressive or gratuitous interference with the rights of those subject to them as could find no justification in the minds of reasonable men, the Court might well say, “Parliament never intended to give authority to make such rules; they are unreasonable and ultra vires.” But it is in this sense, and in this sense only, as I conceive, that the question of unreasonableness can properly be regarded.