No! Often, we hear that a complainant has asked to remain anonymous. It is critical that they be dealt with honestly: it is not possible to guarantee confidentiality, as the accused individual will be entitled to details of the allegations which may implicitly or explicitly reveal who complained, and if the matter goes to litigation, all details are likely to come out. However, many of our clients are able to reassure people by promising to maintain confidentiality to the fullest extent possible and only disclose information when they have to.
That said, parties and witnesses should be warned that they must maintain confidentiality.