Anyone who wants to enter Britain must pass through official border controls; however, sometimes people get into the country illegally. This means they haven’t told the authorities, they do not hold the right documents or they have stayed longer than their visa allows. They are then called an illegal immigrant.
At the Port of Calais in France the police face a constant battle to stop people smuggling themselves into Britain. Many have arrived from poor or war-torn countries and believe they will find a better life in Britain.