The British Board of Film Classification (BBFC) is responsible for regulating films shown in the UK. They assign age ratings to films including U, PG, 12, 12A, 15, and 18 based on the film's content. The BBFC reviews all films and trailers submitted to determine the appropriate rating based on their guidelines for violence, sexual content, language, and more. The document then provides examples of what types of content is acceptable or not for each rating level.