The United Kingdom set its borders by enforcing a set of rules called the Immigration Act or Immigration control before allowing non-UK citizens. These laws are in place to set a limit on the length of their stay including their purpose, if they are allowed to ask their families to join them, and if they could take advantage of the many benefits of the UK.
Immigration law is rather complicated because they are beyond the law of citizenship that includes different types of British nationality and the provisions of what defines British citizenship. You can read more about immigration laws and how the immigration lawyers help you in this over the internet.
The United Kingdom's immigration laws are broadly categorized into two parts and are given to individuals who have the right of abode in the UK and those who require permission to remain or to enter the UK. There are groups of people who somehow do not fit into this category because they have to negotiate with the state attorney if they belong to this group.
There are more than a few immigration laws set in place for an individual or group in this case and the way they are given. This category also includes students, couples, au pairs and visitors. Each category has a set of requirements necessary for the completion and some consideration before a visa is established.
One example is the situation for a student visa in which a student must have a full education in an accredited educational institution in the UK. If these requirements are achieved then the student visa granted.