Victimisation has a specific legal meaning, which is different to it's general use. Victimisation is where an employer subjects a worker to a detriment because the employee has done a 'protected act' or because the employer believes that the employee has done or may do a protected act in the future. A protected act includes:
Bringing legal proceedings under the Equality Act 2010
Giving evidence or information in connection with proceedings brought under the Equality Act 2010
Making an allegation that another person has done something in breach of the Equality Act 2010
The offence exists to prevent employers mistreating or punishing those who have claimed the protection of the law or tried to help others to do so.