You can refer to Wednesbury Unreasonableness (Associated Provincial Picture Houses Ltd. v Wednesbury Corporation, 1948), which established that a decision is considered unreasonable (and thus unlawful) if it is so irrational that no reasonable authority would have made it. A decision to impose a CPZ without resident consent with significant permit costs, but as part of a wider policy agenda, could be challenged under this principle as being irrational.