Gathering your evidence will be an important step, especially if you wish to escalate your complaint. The types of information you should gather should include:
- Recording a timeline of events
- Names of witnesses if relevant
- Copies of documents that support your case such as letters, emails etc.
- Copies of any policies
- How other colleagues are being treated compared to you
Another useful tool which is under utilised is making a Subject Access Requests (SAR) to gather evidence. Subject Access Request is a legal right under data protection laws that allows an individual to request access to the personal data an organisation holds about them. Some employers may in fact try and use data protection laws to refuse to provide personal data - if this happens, make a complaint to the Information Commissioner. The employer should respond within one month of the request being made.
A guide to making a subject access request can be found here:
https://ico.org.uk/for-organisations/uk-gdpr-guidance-and-resources/subject-access-requests/a-guide-to-subject-access/