'In many contexts it will be necessary for a person to demonstrate some particular interest in order to demonstrate that he is not a mere busybody. Not every member of the public can complain of every potential breach of duty by a public body. But there may also be cases in which any individual, simply as a citizen, will have sufficient interest to bring a public authority's violation of the law to the attention of the court, without having to demonstrate any greater impact upon himself than upon other members of the public. The rule of law would not be maintained if, because everyone was equally affected by an unlawful act, no one was able to bring proceedings to challenge it.'