Creating a fairer Britain
Whether you decide that there had been unlawful discrimination or not, make sure that you do not treat the worker who complained badly. For example, forcing the worker who complained to transfer to another part of your organisation (if it is big enough) may amount to victimisation. However, if they ask to be transferred, you should do this if you are sure this is what they really want, and it is not a sign that you have not dealt with their complaint properly.
Monitor the situation to ensure that the unlawful discrimination (if you found there was discrimination) has stopped and that there is no victimisation of the worker who complained or anyone who helped them.
If your worker is not satisfied with what has happened, they may decide to bring a claim in the Employment Tribunal.