illegality (namely, failure to give effect to the law that regulates the decision making power)
irrationality, namely Wednesbury unreasonableness, the question ‘whether or not they [the local authority] have taken into account matters which they ought not to have taken into account, or … have refused to take into account or neglected to take into account matters which they ought to take into account’
procedural impropriety
All of them
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