Build a wall.....
Just to extend Any other name a bit, almost all illegal immigration consists of a person entering a country legally with one type of visa (typically tourist or student), then staying in the country while violating some of the terms of the visa.
The idea that you prevent all illegal immigration at the border is extremely naive. It's how do you police the people once they are in your country, and what do you do when they have effectively settled.
Depending on how they are obtained, a student visa may require you to prove things from your home country first, such as going through a partner university, or may require you to show up in the host country on a tourist visa until the sponsor university is satisfied you can pay, and your grades are real. It also means the university doesn't have to do certain checks, just assumes that you can leave your home country and enter the UK without any other external issues, ie previous convictions.
Biting the hand that feeds IT
