“… first, the Secretary of State is entitled to apply policy applicable as at the date of decision under challenge. Secondly, the court is concerned not with maladministration but only with illegality, so that if maladministration produces a decision that is unlawful, that can be the subject of a successful challenge, but not otherwise. Thirdly, there is no principle of administrative law that if the Secretary of State had made a decision earlier resulting in a more favourable outcome for an individual, then whatever the changed circumstances may be when the decision was actually made, that more favourable decision must be made …”