Start by writing down what happened, including dates, people involved and any effect on you, and keep relevant emails, payslips or other records. Check your contract, workplace policies and the official GOV.UK guidance to understand which rights may apply. If it feels safe, raise the issue with your manager or HR in writing and ask how it will be investigated. You can contact Acas for free guidance; strict time limits may apply if you later consider an employment tribunal, so speak to an employment solicitor regulated by the SRA if the matter is serious.