The reason that this magical policeman was pretending to be a nonmagical MI-5 agent was because of a law called the International Statute of Wizarding Secrecy. This law said, "You are not allowed to tell someone who does not already know that magic is real, the truth about magic." Every magical person on the planet was bound by this law; this law also applied to nonmagical people like Aunt Emma and Uncle Dan—and now the law applied to Beverly herself.