Write down what happened, including dates, people involved and any witnesses, and keep relevant emails, messages and documents. Check your contract, workplace policies and staff handbook, then consider raising the issue informally with your manager or HR, unless this would be unsafe or inappropriate. You can contact Acas for free guidance on workplace rights and resolving disputes; employment tribunal time limits can be short, often three months less one day, so do not delay. For complex matters, consider advice from a trade union or a solicitor regulated by the SRA.