 All staff were, and are, governed by the overarching laws found within the various Immigration and Nationality Acts but the everyday application of the law at ports of entry is made through the application of the Immigration Rules – these are published rules that explain how the law is to be interpreted and applied.It is the interpretation of the rules that make immigration law so controversial.The practicalities of assessing large numbers of people arriving at ports mean that a great deal of discretion is given to the immigration officer, (although less now than was once the case).