An employee steals £20 from the company and the police will come and arrest that person, and they have a good chance to bring a prosecution if they have committ

An employee steals £20 from the company and the police will come and arrest that person, and they have a good chance to bring a prosecution if they have committed a similar crime before. An employer with-holds/steals/defrauds an employee for £500 or more, and not only will the police not care, they won't even note it as a crime. Best bet is a civil court, but that takes time and can cost money. So most people just move on and the employer does it again and again.