Identify all of the complaints constituting the grievance and clarify with the employee if necessary.
Carry out a thorough investigation – check the facts, gather any evidence, identify relevant witnesses to speak to and take witness statements from them.
Consider whether there are any documents which may be relevant to the grievance and consider these in the investigation.
Consider whether there are any issues regarding data protection or confidentiality in relation to disclosing any documents.
Consider whether it is appropriate to inform those employees or third parties who will be interviewed as part of the investigation of the exact detail of the grievance complaints (this will depend on the nature/sensitivity of the grievance and whether or not the employee raising the grievance is still in employment).