Any error in completing customs procedures can result in the visitor's detention. Over 170 million Europeans have received a very clear warning from their governments this week: precautions must be taken when traveling to the United States.

The United Kingdom updated its advice for travel to the United States on Thursday, warning of harsh consequences for British passport holders who violate U.S. immigration laws. The notice comes just a day after Germany updated its travel advice after three of its citizens were detained trying to enter the U.

The United Kingdom could face civil war within the next five years due to the "destruction of legitimacy" caused by the government’s failure to secure the country’s borders, according to a government advisor and leading academic.